Category: Class 10

SCIENCE

SET I

Section – A

Q. 1. Write title number of covalent bonds in the molecule of ethane.

Answer.

 

Q. 2. Name the life process of an organism that helps in the growth of its population.

Answer. Reproduction is the process that helps in the growth of population of an organism.

 

Q. 3. What will be the amount of energy available to the organisms of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 joules?

Answer. According to 10% law, only 10% of energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.

If energy in the 1st trophic level is 10000 J.

Then, energy in 2nd trophic level = 10% of 10000 J = 10/100 x 10000 J = 1000 Joules

 

Q. 4. The absolute refractive indices of glass and water are 4/3 and 3/2 respectively. If the speed of light is 2 x 108 m/s, calculate the speed of light in (i) vacuum, (ii) water.

Answer.

 

Q. 5. List -two main causes of the pollution of water of the river Ganga. State how pollution and contamination of river water prove harmful for the health of the people of neighbouring areas.

Answer. Two main cause of the pollution of water of the river Ganga :

(i) Disposal of industrial effluents into tire river.

(ii) Human activities like bathing, washing, immersion of ashes; etc.

Pollution and contamination of river wafer has led to various harmful effects on health of people in neighbouring areas who use river water for domestic or drinking purposes. It has led to various types of water borne diseases such as typhoid or cholera. Also human and industrial activities have lead to contamination of marine life which can be hazardous for consumption.

 

Q. 6. What is biodiversity? What will happen if biodiversity of an area is not preserved? Mention one effect of it.

Answer. Biodiversity is the diversity of life in an area. It is the number and range of variety of species of life forms in an area.

The loss of biodiversity of an area will lead to the loss of ecological stability of the eco- system. It can result in environment disasters such as floods, forest fires, etc.

 

Q. 7. List two tests for experimentally distinguishing between an alcohol and a carboxylic acid and describe how these tests are performed.

Answer. Test-1—Litmus Test. Take 2 strips of blue litmus paper. Place a drop each of alcohol and carboxylic acid on these strips separately. The blue litmus paper turns red in the case of carboxylic acid and remains unaffected in the case of alcohol.

Test-2—Sodium hydrogen carbonate Test /Sodium carbonate Test. A pinch of sodium hydrogen carbonate or sodium carbonate is added to both alcohol and a carboxylic acid separately. If brisk effervescence with the evolution of a colourless gas is observed, it ! indicates the presence of carboxylic acid whereas no effervescence is seen in case of an alcohol.

 

Q. 8. Draw the electron-dot structure for ethyne. A mixture of ethyne and oxygen is burnt for welding. In your opinion, why cannot we use a mixture of ethyne and air for this purpose?

Answer. In pure oxygen, ethyne undergoes complete combustion and high temperature suitable for welding is attained. Whereas air contains less percentage/amount of oxygen which results in incomplete combustion of ethyne and the temperature required for the welding is not attained. Hence we cannot use a mixture of ethyne and air for this purpose.

 

Q. 9. Two elements ‘P’ and ‘Q’ belong to the same period of the modern periodic table and are in Group-1 and Group-2 respectively. Compare their following characteristics in tabular form:

(a) The number of electrons in their atoms

(b) The sizes of their atoms

(c) Their metallic characters

(d) Their tendencies to lose electrons

(e) The formula of their oxides

(f) The formula of their chlorides

Answer.

Characteristics	P	Q
(a) No. of electrons in their atoms	Less than Q31119	More than P41220  (any one pair)
(b) Size of the atom	Bigger	Smaller
(c) Metallic character	More metallic	Less metallic
(d) Tendency to lose electrons	More	Less
(e) Formula of their oxides	P2O	QO
(f) Formula of their chlorides	PCl	QCl2

 

Q. 10. Taking the example of an element of atomic number 16, explain how the electronic configuration of the atom of an element relates to its position in the modern periodic table and how valency of an element is calculated on the basis of its atomic number.

Answer. Atomic number of the element = 16 Electronic configuration = K L M = 2, 8, 6

Since this element has 3 shells, the period number will be 3 as period number is equal to the number of shells that start filling up in it.

No. of valence electrons = 6

The group number will be 10 + 6 = 16

The valency of an element is determined by the number of valence electrons present in the outermost shell.

Valency of the element will be = 8 – valence electrons = 8-6 = 2

 

Q. 11. List six specific characteristics of sexual reproduction.

Answer. Characteristics of sexual reproduction are:

1. In sexual reproduction, two parents are involved (male and female).
2. The new organism produced is genetically different from both parents.
3. During gamete formation meiosis occurs. After fertilisation all divisions are mitotic.
4. Sexual reproduction helps in evolution.
5. Fertilisation of gametes leads to zygote formation. This zygote grows and develops to form a new organism.
6. Humans, fish, dogs, hens, cats, cows, horses, deer, rabbit, lions and tigers all reproduce by the method of sexual reproduction. Most of the flowering plants also reproduce by sexual reproduction.

 

Q. 12. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.

Answer. Chromosomes are thread-like structures made up of DNA and proteins. They are found in the nucleus at the time of cell division.

During gamete formation meiosis occurs and the original number of chromosomes becomes half. Hence, when two gametes combine the zygote formed contains the full set of chromosomes and the original number of chromosomes gets restored in the progeny.

 

Q. 13. List four points of significance of reproductive health in a society. Name any two areas related to reproductive health which have improved over the past 50 years in our country.

Answer. The significance of reproductive health of society are:

1. Regular medication and check-ups have led to development of reproductive health.Healthy mothers give birth to healthy children.
2. Reproductive health should be maintained in order to prevent sexually transmitted diseases (STDs).
3. Family planning by using various contraceptives enables a couple to decide on the number of children they want to have and when to have them. If a couple has less number of children they can provide good food, clothes and education to each child. So a small family is a happy family.
4.  Having fewer children also keeps the mother in good health. This will reduce the cases of maternal mortality as well as new born mortality.

Areas which have improved:

1. Better family planning has led to reduction in family size and better economic stability.
2. Decrease in STD cases due to more awareness and wider use of contraceptives.

 

Q. 14. Explain with an example for each, how the following provides evidences in favour of evolution in organisms: (a) Homologous organs (b) Analogous organs (c) Fossils

Answer.

(a) Homologous organs : Homologous organs are defined as the organs of different animals that are having a similar structure but differ in their functions. The structure of the two different animals resemble but the functions of their organs vary.

(b) Analogous organs : Analogous organs are defined as the organs of different animals that are having different structure but perform the same functions.

(c) Fossils : Fossils are the preserved remains, or traces of remains, of ancient organisms. Fossils are not the remains of the organism itself! They are rocks.

 

Q. 15. Explain the following:

(a) Speciation (b) Natural Selection

Answer. 

(a) Speciation : Speciation is a process within evolution that leads to the formation of new, distinct species that are reproductively isolated from one another.

Anagenesis, or ‘phyletic evolution’, occurs when evolution acts to create new species, which are distinct from their ancestors, along a single lineage, through gradual changes in physical or genetic traits. In this instance, there is no split in the phylogenetic tree. Conversely, ‘speciation’ or cladogenesis arises from a splitting event, where a parent species is split into two distinct species, often as the result of geographic isolation or another driving force involving the separation of populations.

(b) Natural Selection : Natural selection can be defined as the process through which species adapt to their environment in order to survive. Natural selection occurs when traits that predispose organisms to survive in an environment are passed from parents to their offspring.

• Organisms that are unable to adapt to changes in the environment are unlikely to survive or reproduce.
• Those that can adapt are much more likely not just to survive, but also to thrive and reproduce.
• As offspring are born, they will have the advantageous genetic traits passed on from their parents.
• As a result, the species will change over time.
• Why? Because offspring will develop traits or characteristics that predispose them to do well in their natural environment.

 

Q. 16. If the image formed by a mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a ray diagram to justify your answer. Where and why do we generally use this type of mirror?

Answer. Convex mirror always forms an erect, virtual and diminished image for all positions of the object placed in front of it.

Uses:

1. Convex mirrors are used as rear-view mirrors in vehicles to see the traffic at the rear side (or back side) because —

              (i) a convex mirror always produces an erect image of the object;

              (ii) the image formed in a convex mirror is highly diminished due to which a convex mirror gives a wide field of view.

2. Big convex mirrors are used as ‘shop security mirrors’. By installing a big convex mirror at a strategic point in the shop, the shop owner can keep an eye on the customer to look for thieves and shoplifters among them as convex mirrors always form a virtual, diminished and erect image.

 

Q. 17. What is meant by scattering of light? Use this phenomenon to explain why the clear sky appears blue or the sun appears reddish at sunrise.

Answer. Scattering of light is the phenomenon to throw light in various random directions. Light is scattered when it falls on various types of suspended particles in its path. The colour of the scattered light depends on the size of the scattering particles in the atmosphere.

— The larger particles of dust and water droplets present in the atmosphere scatter the light of longer wavelengths due to which the scattered light appears white.

— The extremely minute particles such as air molecules present in the atmosphere scatter mainly blue light present in the white sunlight.

Colour of the sky appears blue. The molecules of air and other fine particles in the atmosphere have a size smaller than the wavelength of visible light. So these particles scatter more effectively the light rays of shorter wavelength at the blue end than light of longer wavelength at the red end. When the scattered blue light enters our eyes, it gives us the feeling of a blue sky.

Colour of the sun appears red at sunrise and sunset. The sun at sunrise and sunset is very near to the horizon, and near the horizon most of the blue light of shorter wave-lengths is scattered away by the particles in the atmosphere. Therefore, the light that reaches our eyes is of longer wavelengths that gives rise to the reddish appearance of the sun.

 

Q. 18. Differentiate between biodegradable and non-biodegradable substances with the help of one example each. List two changes in habit that people must adopt to dispose non- biodegradable waste, for saving the environment.

Answer. Difference between biodegradable substances and non-biodegradable substances. See Q. 2, 2011 (II Outside Delhi).

Habits for disposing non-biodegradable waste:

1. Disposal of wastes after separating them into biodegradable and non-biodegradable wastes in separate dustbins and treating wastes properly before dumping in landfills.
2. Encourage the use of gunny bags, jute bags and paper bags in place of polythene/ plastic bags.
3. Recycle the plastic and glass objects after use.

 

Q. 19. Both soap and detergent are some type of salts. What is the difference between them? Describe in brief the cleansing action of soap. Why do soaps not form lather in hard water? List two problems that arise due to the use of detergents instead of soaps

Answer.

A soap is the sodium or potassium salt of a long chain carboxylic acid.

Example : C₁₇H₃₅ COO^– Na⁺              Sodium stearate

                   C₁₅H₃₁ COO^– Na⁺              Sodium palmitate

A detergent is ammonium or sulphonate salt of a long chain carboxylic acid.

Example : CH₃ – (CH₂)₁₁ – C₆H₄ – SO₃^– Na⁺

                    CH₃ – (CH₂)₁₀ – CH₂ – SO₄^– Na⁺

Cleansing Action of Soaps :Most of the dirt is oily in nature and oil does not dissolve in water. The molecule of soap constitutes sodium or potassium salts of long-chain carboxylic acids. In the case of soaps, the carbon chain dissolves in oil and the ionic end dissolves in water. Thus, the soap molecules form structures called micelles. In micelles, one end is towards the oil droplet and the other end which is the ionic faces outside. Therefore, it forms an emulsion in water and helps in dissolving the dirt when we wash our clothes.

Soap is a kind of molecule in which both the ends have different properties.

• Hydrophilic end
• Hydrophobic end

The first one is the hydrophilic end which dissolves water and is attracted to it whereas the second one is the hydrophobic end that is dissolved in hydrocarbons and is water repulsive in nature. If on the surface of the water, soap is present then the hydrophobic tail which is not soluble in water will align along the water surface.

Soaps don’t form lather in hard water

Soap is sodium or potassium salt of certain long chain fatty acids such as stearic acid, palmitic acid, oleic acid etc. When hard water is treated with soap solution, Ca2+and Mg2+ ions present in hard water react with the anions of fatty acids present in the soap to form a scum (curdy white precipitate).

Ca²⁺(aq) + 2C₁₇H₃₅COO^–(aq)   →  (C₁₇H₃₅COO)₂ Ca ↓

Mg²⁺(aq) + 2C₁₇H₃₅COO^–(aq)   →  (C₁₇H₃₅COO)₂ Mg ↓

Soap will not produce a lather with hard water until all the calcium and magnesium ions have been precipitated as stearates. Hard water thus wastes soap.

Problems that arise due to the use of detergents instead of soaps:

1. Detergents are non-biodegradable, i.e., they cannot be decomposed organisms and hence cause water pollution in lakes and rivers.
2. Detergents can also cause skin problems.

 

Q. 20. (a) Name the human male reproductive organ that produces sperms and also secretes a hormone. Write the functions of the secreted hormone.

(b) Name the parts of the human female reproductive system where

(i) fertilisation takes place,

(ii) implantation of the fertilised egg occurs.

Explain how the embryo gets nourishment inside the mother’s -body.

Answer. (a) Testis produces sperms and secretes male hormone—testosterone.

Function of testosterone hormone is to control the development of male sex organs and male features such as deeper voice, moustaches, body hair, etc. All these changes caused by testosterone are associated with male puberty which the boys attains at an age of 13 to 14 years. It also controls the formation of male gamete, i.e., sperm.

(b) (i) Fertilisation takes place in fallopian tube (oviduct).

(ii) Implantation of the fertilised egg occurs in the uterus.

Nourishment of embryo. After fertilisation, zygote is formed which develops into an embryo. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. In this way, embryo gets its nutrition.

 

Q. 21. How do Mendel’s experiments show that the

(a) traits may be dominant or recessive,

(b) traits are inherited independently?

Answer. Mendel’s experiments show that the

(a) Traits may be dominant or recessive. When Mendel cross-bred plants of two different traits of character, a tall pea plant (TT) and a dwarf pea plant (tt) to get a progeny ( F1 generation), all F1 plants were tall. Only the dominant trait was visible in this generation. But when plants of F1 generation were self bred then the two traits of character got separated in the plants of F2 generation. All plants obtained in the F2 generation were not tall. One-fourth of the F2 plants were short.

Appearance of tall characters in both the F1 and F2 generations shows that it is a dominant character. Whereas the absence of dwarf character in F1 generation and its reappearance in F2 generation shows dwarfness is the recessive character.

(b) Traits are inherited independently. Mendel cross-bred pea plants showing two different characteristics, rather than just one. When he cross-bred pea plants of round green seeds with wrinkled yellow seeds, he got F1 generation with all such seeds which were Gametes yellow and round. So, it was concluded that round and yellow character of seeds were dominant traits in the pea plant. On selfing of F1 progeny, different types of F2 progeny were obtained.

So traits of two different characters were inherited independent of each other and made new combination characteristics independent of their previous combinations.

Q. 22. What is meant by power of a lens? Define its S.I. unit. You have two lenses A and B of focal lengths +10 cm and 10 cm respectively. State the nature and power of each lens.Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens? Draw a ray diagram to justify your answer.

Answer.

Power of the lens is known as the inverse of the focal length of the lens measured in meter(m).

S.I unit of power = Dioptre (D)

Power of lense = 1/ focal length in meter.

The lense used is a convex lens because the focal length is a positive value.

Lens A: F_A = +10 cm = +10/100 = 0.1 m

    P_A = 1/F_A = 1/+0.1 = +10 D

The power of a convex lens is positive therefore, lens A is a convex lens.

Lens B: F_B = -10 cm = -10/100 = 0.1 m

    P_B = 1/F_B = 1/-0.1 = -10 D

The power of a concave lens is negative therefore, lens B is a concave lens.

When an object is placed at 8 cm (i.e., between the optical centre and principal focus) only convex lens will form the virtual and magnified image.

Therefore, lens A will form a virtual and magnified image of the object placed 8 cm from it. When the object is placed between the optical centre and the focus: (i.e., between O and F) the image formed is behind the object (on the same side), virtual, erect and magnified.

 

Q. 23. One half of a convex lens of focal length 10 cm is covered with a black paper. Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray diagram to justify your answer.

A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find nature, position and size of the image.

Answer. (i) Yes. If a convex lens of focal length 10 cm is covered one half with a black paper, it can produce an image of the complete object between F2 and 2F2. The rays of light coming from the object get refracted by the upper half of the lens. The image formed will be real, inverted and diminished.

Q. 24. Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles in old age. What type of lenses are required by the persons suffering from this defect to see the objects clearly? Akshay, sitting in the last row in his class, could not see clearly the words written on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.

In the context of the above event, answer the following questions:

(a) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?

(b) State the values displayed by the teacher and Salman.

(c) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?

Answer. Importance of ciliary muscles. The focal length of eye lens can be changed by changing its shape by the action of ciliary muscles. Ciliary muscles modify the curvature of the eye lens to enable the eye to focus objects at varying distances.

In old age, ciliary muscles become weak and the eye lens become inflexible. As a result, the eye loses its power of accommodation. Because of this, an old person cannot see the nearby objects clearly. This leads to the defect called presbyopia.

Bifocal lenses are required by the persons suffering from presbyopia in which upper part consists of a concave lens for distant vision and the lower part consists of a convex lens used to see nearby objects.

(a) Akshay is suffering from myopia or near sightedness. Myopia is corrected by using spectacles containing concave lenses. The concave lens used for correcting myopia should be of such a focal length that it produces a virtual image of the distant object (lying at infinity) at the far point of the myopic eye.

(b) • The teacher is concerned about the health of the student.

• Salman is very helpful and caring.

(c) Akshay should express his gratitude towards his teacher as well as his friend Salman by getting his eyesight checked and by also following their values in his own life.

SECTION B

Q. 25. What do we observe on pouring acetic acid on red and blue litmus papers?

(A) Red litmus remains red and blue litmus turns red.

(B) Red litmus turns blue and blue litmus remains blue.

(C) Red litmus turns blue and blue litmus turns red.

(D) Red litmus becomes colourless and blue litmus remains blue.

Answer. (A)

 

Q. 26. While preparing soap a small quantity of common salt is generally added to the reaction mixture of vegetable oil and sodium hydroxide. Which one of the following may be the purpose of adding common salt?

(A) To reduce the basic nature of the soap

(B) To make the soap neutral

(C) To enhance the cleansing power of the soap

(D) To favour the precipitation of the soap

Answer. (D)

 

Q. 27. A student takes about 4 mL of distilled water in four test tubes marked P, Q, R and S. He then dissolves in each test tube an equal amount of one salt in one test tube, namely sodium sulphate in P, potassium sulphate in Q, calcium sulphate in R and magnesium sulphate in S. After that he adds an equal amount of soap solution in each test tube. On shaking each of these test tubes well, he observes a good amount of lather (foam) in the test tubes marked

(A) P and Q (B) Q and R (C) P, Q and S (D) P, R and S

Answer. (A)

 

Q. 28. A student was asked to observe and identify the various parts of an embryo of a red kidney bean seed. He identified the parts and listed them as under:

I. Tegtnen II. Testa III. Cotyledon IV. Radicle V. Plumule

The correctly identified parts among these are:

(A) I, II and III (B) II, III and IV (C) III, IV and V (D) I, III, IV and V

Answer. (C)

 

Q. 29. Given below is the list of vegetables available in the market. Select from these the two vegetables having homologous structures: Potato, sweet potato, ginger, radish, tomato, carrot, okra (Lady’s finger)

(A) Potato and sweet potato (B) Radish and carrot

(C) Okra and sweet potato (D) Potato and tomato

Answer. (B)

 

Q. 30. A student obtains a sharp image of the distant window (W) of the school laboratory on the screen (S) using the given concave mirror (M) to determine its focal length. Which of the following distances should he measure to get the focal length of the mirror?

(A) MW (B) MS

(C) SW (D) MW-MS

Answer. (B)

 

Q. 31. A student used a device (X) to obtain/focus the image of a well illuminated distant building on a screen (S) as shown below in the diagram. Select the correct statement about the device (X).

(A) This device is a concave lens of focal length 8 cm.

(B) This device is a convex mirror of focal length 8 cm.

(C) This device is a convex lens of focal length 4 cm.

(D) This device is a convex lens of focal length 8 cm.

Answer. (D)

 

Q. 32. A student traces the path of a ray of light through a rectangular glass slab for the different values of angle of incidence. He observes all possible precautions at each step of the experiment. At the end of the experiment, on analysing the measurements, which of the following conclusions is he likely to draw?

(A) ∠z = ∠e < ∠r (B) ∠z < ∠e < ∠r (C) ∠z > ∠e > ∠r (D)∠z = ∠e > ∠r

Answer. (D)

 

Q. 33. A student traces the path of a ray of light through a triangular glass prism for different values of angle of incidence. On analyzing the ray diagrams, which one of the following conclusions is he likely to draw?

(A) The emergent ray is parallel to the incident ray.

(B) The emergent ray bends at an angle to the direction of the incident ray.

(C) The emergent ray and the refracted ray are at right angles to each other.

(D) The emergent ray is perpendicular to the incident ray.

Answer. (B)

 

Q. 34. When you add sodium hydrogen carbonate to acetic acid in a test tube, a gas liberates immediately with a brisk effervescence. Name this gas. Describe the method of testing this gas.

Answer. When sodium hydrogen carbonate is added to acetic acid in a test tube, then a brisk effervescence is observed due to the liberation of CO2 gas which is colourless and odourless.

 

Q. 35. Students were asked to observe the permanent slides showing different stages of budding in yeast under high power of a microscope.

(a) Which adjustment screw (coarse/fine) were you asked to move to focus the slides ?

(b) Draw three diagrams in correct sequence showing budding in yeast.

Answer. (a) A fine adjustment screw is moved to focus the slides.

 

Q. 36. A 4 cm tall object is placed on the principal axis of a convex lens. The distance of the object from the optical centre of the lens is 12 cm and its sharp image is formed at a distance of 24 cm from it on a screen on the other side of the lens. If the object is now moved a little away from the lens, in which way (towards the lens or away from the lens) will he have to move the screen to get a sharp image of the object on it again? How will the magnification of the image be affected?

Answer. (a) The screen should be moved towards the lens to get a sharp image of the object again. (b) Magnification of the image decreases on moving the object away from the lens.

SET II

SECTION A

Q. 1. Write the number of covalent bonds in the molecule of propane, C₃H₈.

Answer.

Q. 2. Where is DNA found in a cell?

Answer. DNA is found in the nucleus of the cell.

 

Q. 3. The first trophic level in a food chain is always a green plant. Why?

Answer. The first trophic level in a food chain is always a green plant because green plants have a mechanism for trapping solar energy with the help of their green pigment called chlorophyll and convert it into chemical energy which is stored as carbohydrates in the plant for the use of the next tropic level.

 

Q. 5. We often observe domestic waste decomposing in the by lanes of our homes. List four ways to make the residents aware that the improper disposal of wastes is harmful to the environment and also for their own health.

Answer. The various ways to make residents aware of the harmful effects of improper disposal of wastes are as follows:

1. By putting posters and hoardings.
2. By distributing pamphlets to the residents.
3. By conducting meetings of residents, welfare society, etc.
4. By advertisements through TV/radio/cable operators, etc.
   Through all these mediums we can make the residents aware of how such waste serves as a breeding ground for mosquitoes, releases harmful gases, reduces soil fertility, etc.

 

Q. 6. List any two advantages associated with water stored in the ground.

Answer. Advantages of underground water:

1. The water stored in the ground does not evaporate.
2. The water stored in the ground does not promote breeding of mosquitoes.

 

Q. 7. What is meant by homologous series of carbon compounds? Classify the following carbon compounds into two homologous series and name them.

C3H4 C4H6, C4H8, C5H8, C5H10

Answer. A homologous series is a group of organic compounds having similar structure and similar chemical properties in which the successive compounds differ by CH2 group.

 

Q. 9. The elements 4Be, 12Mg and 20Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements, giving reason in each case:

(a) In which group should they be?

(b) Which one of them is least reactive?

(c) Which one of them has the largest atomic size?

Answer.

(a) They all belong to 2nd group of the periodic table as all the elements have two valence electrons in their valence shell.

(b) Be is least reactive as it contains the least number of shells (i.e., 2). The tendency of an atom to lose electrons on moving down in a group increases as valence electrons move more and more away from the nucleus and nuclear charge on valence electrons decreases.

(c) Ca has the largest atomic size as it has the maximum number of shells.

 

Q. 11. List three distinguishing features between sexual and asexual types of reproduction, in tabular form.

Answer.  Difference between Sexual and Asexual types of reproductions

Sexual Reproduction	Asexual Reproduction
Two parents are involved	One parent is involved
Characteristics of both parents are inherited	Characteristics of only one parent are inherited
It requires the formation of gametes	It doesn’t require the formation of gametes
Special organs for reproduction are required.	Special organs for reproduction are not required
Examples – Mangoes, coconut, Hibiscus etc.	Examples – Potato, Jasmine, Rose, Yeast, Bryophyllum etc

 

Q. 14. A pea plant with blue colour flower denoted by BB is crossbred with a pea plant with white flower denoted by ww.

(a) What is the expected colour of the flowers in their F4 progeny?

(b) What will be the percentage of plants bearing white flower in F2 generation, when the flowers of F4 plants were selfed?

(c) State the expected ratio of the genotype BB and Bw in the F2 progeny.

Answer.

 

Q. 18. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain.

Answer. An ecosystem is a self-contained unit of living things (plants, animals and decomposers) and their non-living environment (soil, air and water). An ecosystem needs only the input of sunlight energy for its functioning.

Ecosystem is made up of two main components:

(i) Abiotic component meaning non-living component.

(ii) Biotic component meaning living component.

An aquarium is an artificial ecosystem. It needs to be cleaned regularly because it has – stagnant water and no decomposers. Therefore the dead parts and excrete of the organisms of the aquarium are not decomposed and would never be returned to their original pool. The accumulation of these wastes can be dangerous for the living organisms in the aquarium.

 

Q. 19. What are fossils? How are they formed? Described in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.

Answer. 

Fossils : fossils are the remains of organisms found in the earth’s strata (rock layers). These organisms have, in some way, been protected from the bacterial action that degrades carbon-based organisms.

Fossils are created through sudden disruptions, like earthquakes. They can also be formed through steadier processes, like exposure to the (extreme) elements.

In most cases, the environment plays a direct role, as a preservative, in whether an organism will become a fossil.

The ideal environment is silty, with moving sediment that can cover the organism. The floors of oceans, lakes, and deep ponds are prime spots for fossilization.

Imagine a sick dinosaur pulling itself to a lake for a drink. It dies. The body falls in and sinks to the bottom. The lake’s motion deposits mud and sand on the animal.

Over time, the soft tissues dissolve, and the mineral-rich sediment fills the gaps. Years pass and the minerals harden around the bones, creating a petrified structure we’ve come to know as fossils.

• The age of the fossils can be determined by the following way:

1. Radiometric dating :In this method, the age of the fossil can be determined by tracing the radioactive elements present in the rocks and examining it chemically.

2. Relative dating :The fossils are found in the sedimentary rocks in the form of layers accumulated over large span of time. So, using this fact, the geologist find the age of fossils in the way that the fossil found at the bottom of those layers are found to be older than that found above those.

3. Fossils have a significant role in evolution as they help in creating evolutionary relationships with the earlier organisms and the present day organisms.

 

SET III

Q. 1. Write the number of covalent bonds in the molecule of butane, C₄H₁₀.

Answer.

 

Q. 2. Name two simple organisms having the ability of regeneration.

Answer. Two simple organisms having the ability of regeneration are Planaria and Hydra.

 

Q. 3. Which of the following are always at the second trophic level of food chains? Carnivores, Auto trophs, Herbivores

Answer. Herbivores are always at the second trophic level of food chains.

 

Q. 4. Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray of light parallel to the principal axis of a convex mirror and show the angle of incidence and angle of reflection on it.

Answer. 

Q. 5. Why is sustainable management of natural resources necessary? Out of the two reuse and recycle which, in your opinion, is better to practise? Give reason.

Answer. Sustainable management is management that encourages the judicious use of natural resources to meet the current basic human needs while preserving the resources for the needs of future generations.

Reuse is a better practise than recycle as recyling requires a large amount of energy and money. In this strategy, we are encouraged to use things again and again instead of throwing them away with no expense of energy. Reuse also does not cause pollution. Example, plastic bottles of jams and pickles can be reused for storing things in the kitchen.

 

Q. 7. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen is possible. State the essential condition for an addition reaction. Stating this condition, write a chemical equation giving the name of the reactant and the product of the reaction.

Answer. Addition of hydrogen is possible in Alkenes C_nH_2n and Alkynes C_nH_2n-2

• Addition reaction of unsaturated hydrocarbons occurs in the presence of catalysts such as nickel (Ni) or palladium (Pd) or platinum (Pt) to form saturated hydrocarbons.
• Example, Ethene reacts with hydrogen when heated in the presence of nickel catalyst to form ethane.
  

 

Q. 9. Given below are some elements of the modern periodic table. Atomic number of the element is given in the parentheses: A(4), B(9), C(14), D(19), E(20)

(a) Select the element that has one electron in the outermost shell. Also write the electronic configuration of this element.

(b) Which two elements amongst these belong to the same group? Give reason for your answer.

(c) Which two elements amongst these belong to the same period? Which one of the two has bigger atomic radius?

Answer.

(a) D has 1 electron in the-outermost shell. Atomic no. = 19, Elec. Configuration = 2, 8, 8,1

(b) A and E belong to the same group, i.e., 2nd group of the periodic table as both have same number of valence electrons (i.e., 2) in their outermost shell.

(c) A & B and D &’E belong to the same period as they have the same no. of valence shells. A and B have 2 shells thus belong to 2nd period of the periodic table.

D and E have 4 shells thus belong to 4th period of the periodic table.

A has the bigger atomic radius among A and B and D has the bigger atomic radius among D and E as atomic size decreases on moving from left to right in a period (or atomic size decreases as the atomic number increases in a period).

 

Q. 12. List four categories of contraceptive methods. State in brief two advantages of adopting such preventive methods.

Answer.  The contraceptive methods can be broadly classified into the following categories:

1. Natural method: It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because, during this period, ovulation is expected and therefore, the chances of fertilization are very high.

2. Barrier method: In this method, the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.

3. Oral contraceptives: In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.

4. Implants and surgical methods: Contraceptive devices such as the loop or Copper-T are placed in the uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.

Advantages of adopting such preventive methods:

1. Contraceptive methods are used to prevent the spread of sexually transmitted diseases like syphilis, AIDS, etc.
2. Contraceptives prevent unwanted and frequent pregnancies. If a couple has less number of children, they can provide good clothes, good food and a good education to each child. This will make the parents as well as children happy.

 

Q. 17. An object of height 5 cm is placed perpendicular to the principal axis of a concave lens of focal length 10 cm. If the distance of the object from the optical centre is 20 cm, determine the position, nature and size of the image formed using the lens formula.

Answer.

Science

SET I

Section – A

Q. 1. Write the name and structure of an alcohol with three carbon atoms in its molecule.

Answer. Name of an alcohol: Propanol

 

Q. 2. What happens when a mature spirogyra filament attains considerable length?

Answer. When a mature spirogyra filament attains considerable length, it breaks up into smaller fragments or pieces, and each fragment grows into a new filament or individual.

 

Q. 3.  The depletion of the ozone layer is a cause of concern. Why?

Answer. The depletion of the ozone layer is a cause of concern because ozone shields the surface of the earth from harmful ultraviolet radiations coming from the Sun. These radiations are very harmful and can cause skin cancer and other health problems in human beings. Moreover, ozone protects the ecosystem from damage.

 

Q. 4. Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device.

Answer. Concave mirrors are used in the design of solar furnaces. When a solar furnace is placed at the focus of a large concave mirror (called reflector), it focuses a parallel beam of light on the furnace, as a result a temperature is achieved after some time.

 

Q. 5. “What was Chipko Andolan”? How did this Andolan ultimately benefit the local people and the environment?

Answer. Chipko Movement. Chipko Movement is an example of the contribution of common people towards the conservation of forests. The Chipko Movement also called ‘Hug the tree’ movement originated from an incident in a remote village called ‘Reni’ in Garhwal (Himalayas), where the people of this village clasped the tree trunks with their arms to protect them from being cut down by a contractor’s workers. The people acted this way because they knew that this mass deforestation would spoil their healthy environment. The forest trees were thus saved.

The Chipko Movement quickly spread across all the communities and helped in the conservation of forests and thus helped in safeguarding the environment.

 

Q. 6. “Burning of fossil fuels results in global warming”. Give reasons to justify this statement.

Answer. When fossil fuels (coal and petroleum based fuels like petrol, diesel etc.) are burnt, they produce C0₂, CO, water vapours, S0₂, oxides of nitrogen.

Though C0₂ is not a poisonous gas but it is a greenhouse gas which traps the sun’s heat energy falling on the earth. The burning of more and more of fossil fuels is increasing the amount of carbon dioxide in the atmosphere causing increased greenhouse effect leading to global warming.

 

Q. 7. Write chemical equation of the reaction of ethanoic acid with the following:

(a) Sodium; (b) Sodium hydroxide; (c) Ethanol

Write the name of one main product of each reaction.

Answer.

 

Q. 8. An aldehyde as well as a ketone can be represented by the same molecular formula, say C₃H₆O. Write their; language of science.

Answer.

They are called isomers because both have the same molecular formula but different structural formulas (having different functional groups).

 

Q. 9. An element ‘X’ belongs to the 3rd period and group 16 of the Modern Periodic Table.

(a) Determine the number of valence electrons and the valency of ‘X’.

(b) Molecular formula of the compound when ‘X’ reacts with hydrogen and write its electron dot structure.

(c) Name the element ‘X’ and state whether it is metallic or non-metallic.

Answer.

 

Q. 10. An element ‘X! has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’. 

Answer. ‘X’

Mass number 5= 35 No. of neutrons = 18

Atomic number of X = Mass number – Number of neutrons = 35 – 18 = 17

K L M

Thus, electronic configuration of X = 2, 8, 7

Group number = 17th    Period number = 3rd

Valency = 8-7 = 1

 

Q. 11. Define reproduction. How does it help in providing stability to the population of species?

Answer. The production of new organisms from the existing organisms of the same species is known as reproduction. It is essential for the survival of a species on earth. It helps in replacing the lost section of the population due to death and various other causes.

• Populations of organisms live in well defined places called niches in the ecosystem using their ability to reproduce.
• Reproduction involves DNA copying which is the source of information for making proteins thereby controlling body design.
• These body designs allow the organism to use a particular niche for the stability of the population of a species.
• Minor variations may also lead to the stability of the species.

 

Q. 12. Explain the term “Regeneration” as used in relation to reproduction of organisms. Describe briefly how regeneration is carried out in multicellular organisms like Hydra.

Answer. Regeneration is a mode of asexual reproduction in some organisms. The process of getting back a full organism from its body parts is called regeneration. The simple multicellular animals like hydra and planaria show regeneration.

Regeneration in hydra:

• If the body of hydra gets cut into a number of pieces, then each body piece can regenerate into a complete hydra by growing all the missing parts.
• The regeneration of an organism from its cut body part occurs by the process of growth and development.
• The cells of cut body parts divide rapidly to make a ball of cells.
• The cells then become specialised to form different types of tissues which again form various organs and body parts.

 

Q. 13. (a) List two reasons for the appearance of variations among the progeny formed by sexual reproduction.

(b)

(i) Name the part marked ‘A’ in the diagram.

(ii) How does ‘A’ reach part ‘B’?

(iii) State the importance of part ‘C.

(iv) What happens to the part marked ‘D’ after fertilization is over?

Answer. (a) The appearance of variations among the progeny formed by sexual reproduction is due to the following reasons:

(i) Sexual reproduction takes place by the combination of two germ cells produced by two different individuals. Fusion of the male and female gametes.

(ii) Each time zygote is formed by the new combination of variants.

(b) (i) A => Pollen grains .

(ii) Pollen grains, i.e., ‘A’ reach part ‘B’, i.e., stigma of the carpel by the process of pollination.

Pollination is carried out by insects (like bees, butterfuly, etc.), birds, wind, water, etc.

(in) ‘C’ => Pollen tube Pollen tube grows downward through the style towards the female gamete in the ovary. Pollen tube helps the male gamete reach the egg or ovule (female gamete).

(iv) ‘D’ => Fertilised egg or Zygote . The fertilized egg (or zygote) divides several times to form an embryo within the ovule.

 

Q. 14. How does Mendel’s experiment show that traits are inherited independently?

Answer. Gregor Mendel conducted a different series of experiments on the pea plant that helped to deduce the basis of the hereditary rules in living organisms. He worked on how the traits or characters can be passed from one generation to the other. He studied the inheritance pattern in the common pea plant, Pisum sativum. He selected seven pairs of contrasting characters which were present in the parent plants. The plants selected by Mendel were pure breeding pea plants and they showed one form of a trait after fertilization. 

During the experiment, Mendel then crossed these pure breeding lines of the pea plants. When two pairs of contrasting characters were selected during cross, it was known as the dihybrid cross. The dihybrid cross was allowed to fertilize. Mendel selected pea plants with dihybrid seed characteristics such as yellow colored and round seeds and green colored wrinkled seeds. The plants with yellow colored round seeds were crossed with plants with green colored wrinkled seeds. After the cross in the F2 generation, the offspring obtained were with both the parental traits and with two recombinant phenotypes such as yellow round and green wrinkled and another recombinant phenotype with green round and yellow wrinkled. Thus, in the F2 generation all the characters were inherited and the characters were round yellow, round green, wrinkled yellow and wrinkled green.

The obtained traits or characteristics of the phenotypes obtained in the F2 generations indicates original parental combinations are separated which in the process gets inherited independently by the offspring in the next generations.

Note:Mendel selected seven pairs of contrasting characters which he used to experiment with for the inheritance of characteristics in the offspring. In a dihybrid cross, Mendel selected two pairs of contrasting characters and they were crossed. The resultant cross showed the segregation of the traits of both the parents which indicated that the traits were inherited independently. 

 

Q. 15. “Two areas of study namely ‘evolution’ and ‘classification’ are interlinked”. Justify this statement.

Answer. Classification of organisms is based on relative similarities and differences in their internal and external structures. Similarities among organisms will allow us to group them and study the groups and classify them. Some basic characteristics will be shared by most organisms. The more characteristics the two species will have in common, the more closely they are related. The more closely they are related, the more recently they have had a common ancestor. So we can say that classification of a species is in fact a reflection of their evolutionary relationship.

 

Q. 16. The image of an object formed by a mirror is real, inverted and is of magnification -1. If the image is at a distance of 40 cm from the mirror, where is the object placed? Where would the image be if the object is moved 20 cm towards the mirror? State reason and also draw ray diagram for the new position of the object to justify your answer.

Answer.

 

Q. 17. Describe an activity to show that the colours of white light splitted by a glass prism can be recombined to get white light by another identical glass prism. Also draw a ray- diagram to show the recombination of the spectrum of white light.

Answer. i) When a glass prism is used to obtain a spectrum of sunlight, a second identical prism in an inverted position is kept with respect to the first position.

ii) The inverted second prism will allow all the colours of the spectrum to recombine.

iii) Thus a beam of white light will emerge from the other side of the second prism.

Recombination of the spectrum of white light is as shown below:

 

Q. 18. The activities of man had adverse effects on ail forms of living organisms in the biosphere. Unlimited exploitation of nature by man disturbed the delicate ecological balance between the living and nonliving components of the biosphere. The unfavorable conditions created by man himself threatened the survival not only of himself but also the entire living organisms on the mother earth. One of your classmates is an active member of ‘Eco-club’ of your school which is creating environmental awareness amongst the school students, spreading the same in the society and also working hard for preventing environmental degradation cf the surroundings.

(a) Why is it necessary to conserve our environment?

(b) State the importance of green and blue dust-bins in the safe disposal of the household waste.

(c) List two values exhibited by your classmate who is an active member of Eco-clubof your school.

Answer. (a) It is necessary to conserve our environment because of the following reasons:

(i) To save natural resources like air, water and soil from pollution which are essential for our survival.

(ii) To maintain ecological balance in nature.

(iii) The environment provides us fresh air to breathe, a number of useful products such as wood, paper, medicines, etc. The ozone layer of the environment also protects us from harmful ultraviolet radiations from the sun.

(b) Green dustbins are used for biodegradable wastes, and Blue dustbins are used for non-biodegradable wastes.

Importance of two types of dustbins:

(i) Disposal of wastes after separating them into biodegradable and non- biodegradable wastes in separate dustbins and treating wastes properly before dumping in landfills.

(ii) Segregation of biodegradable and non-biodegradable wastes occur without wasting time and energy.

(c) Values: Cooperative spirit, concern about environment, civic sense, sensitive human being.

 

Q. 19. A carbon compound ‘P’ on heating with excess cone. H2S04 forms another carbon compound ‘Q’ which on addition of hydrogen in the presence of nickel catalyst forms a saturated carbon compound ‘R’. One molecule of ‘R’ on combustion, forms two molecules of carbon dioxide and three molecules of water. Identify P, Q and R and write chemical equations for the reactions involved.

Answer.

 

Q. 20. What is placenta? Describe its structure. State its functions in case of a pregnant human female.

Answer. Placenta. It is a special tissue that helps human embryo in obtaining nutrition from mother’s blood. It serves as a link between the mother’s body and the baby.

Structure and function. After fertilisation, zygote is formed which develops into an embryo. The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. This is a disc which is embedded in the uterine wall. It contains thousands of villi on the embryo’s side of the tissue, on the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose, nutrients and oxygen to pass from the mother to the embryo. In this way, embryo gets its nutrition. The wastes produced by the foetus are also removed through the placenta. It also functions as an endocrine gland and secretes hormones necessary for maintaining pregnancy.

 

Q. 21. Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.

Answer. Evolution. Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced.

How it occurs? 

• It is through the constant process of evolution taking place in the organisms since the origin of life that such an enormous variety of plants and animals have come to exist on this earth at present.
• There is an inbuilt tendency to variation during reproduction due to errors in DNA copying and as a result of sexual reproduction.

Relationship between fossils and evolution:

• Fossils are the remains of impressions of dead plants or animals which died millions of years ago. The study of fossils helps us to know about the evolution of species. Fossils tell us how new species are developed from the old. Fossils provide evidence of evolution by revealing characteristics of past organisms and the changes that have occurred m these organisms to give rise to present organisms Therefore, fossils have an importance in deciding evolutionary relationship.
• For example, a fossil called Archaeopteryx has feathered wings like birds but teeth and tail like reptiles hence suggesting that birds and reptiles had a common ancestor.

 

Q. 22. It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.

(i) What should be the range of distance of an object placed in front of the mirror?

(ii) Will the image be smaller or larger than the object? Draw a ray diagram to show the formation of image in this case.

(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror?

Draw a ray diagram for this situation also to justify your answer.

Show the positions of the pole, the principal focus and the centre of curvature in the above ray diagrams.

Answer. In a concave mirror an erect image w ill be obtained when the object is placed between pole and focus ; of the mirror.

Focal length, f = 12 cm

(i) Therefore, the range of object distance is between 0 cm to <12 cm (from zero to less than 12 cm).

(ii) Image formed wall be magnified, i.e., larger than the object.

(iii) If the object is placed at 24 cm in from of the mirror, it means that object is placed at 2f, i.e., at the centre of curvature (at C) of the mirror.

The real, inverted and same size (of the object) image will also be formed at 24 cm.

 

Q. 23.(a) Define optical centre of a spherical lens.

(b) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of the image also.

(c) Draw a ray diagram to show the formation of image in above situation.

Answer. (a) Optical centre of the lens. It is a point within the lens that lies on the principal axis through which avay of light passes undeflected.

 

Q. 24. What is atmospheric refraction? Use this phenomenon to explain the following natural events.

(a) Twinkling of stars (b) Advanced sun-rise and delayed sun-set

Draw diagrams to illustrate your answers.

Answer. Atmospheric refraction. The refraction of light caused by the earth’s atmosphere having air layers of varying optical densities is called atmospheric refraction.

(a) Twinkling of stars. 

The twinkling of a star is due to atmospheric refraction of starlight. 

The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. 

The atmospheric refraction occurs in a medium of gradually changing refractive index. 

Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position. 

The star appears slightly higher (above) than its actual position when viewed near the horizon 

Since the stars are very distant, they approximate point-sized sources of light. As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering eye flickers -the star sometimes appear brighter and sometimes fainter ,which is twinkling effect.

(b) Advanced sun-rise and delayed sun-set. 

The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction. By actual sunrise, we mean the actual crossing of the horizon by the Sun. The time difference between actual sunset and the apparent sunset is about 2 minutes. The apparent flattening of the Sun’s disc at sunrise and sunset is also due to the same phenomenon. 

SCATTERING OF LIGHT 

It is the phenomena of change in direction of light on striking an obstacle like an atom, a molecule a dust particle water droplet etc.

It is also due to atmospheric refraction that we can still see the sun for about 2 minutes even after the sun has set below the horizon. At sunset, the apparent position of the sun is visible to us and not the actual position because of the bending of light rays effect.

So, the time from sunrise to sunset is lengthened by about 2 + 2 = 4 minutes because of atmospheric refraction.

SECTION B

Q. 25. A student puts a drop of reaction mixture of a saponification reaction first on a blue litmus paper and then on a red litmus paper. He may observe that:

(a) There is no change in the blue litmus paper and the red litmus paper turns white.

(b) There is no change in the red litmus paper and the blue litmus paper turns red.

(c) There is no change in the blue litmus paper and the red litmus paper turns blue.

(d) No change in colour is observed in both the litmus papers.

Answer. (c)

 

Q. 26. For preparing soap in the laboratory we require an oil and a base. Which of the following combination of an oil and a base would be best suited for the preparation of soap?

(a) Castor oil and calcium hydroxide (b) Turpentine oil and sodium hydroxide

(c) Castor oil and sodium hydroxide (d) Mustard oil and calcium hydroxide

Answer. (c)

 

Q. 27. In the neighborhood of your school, hard water required for an experiment is not available. Select from the following groups of salts available in your school, a group each member of which, if dissolved in distilled water, will make it hard:

(a) Sodium chloride, calcium chloride (b) Potassium chloride, sodium chloride

(c) Sodium chloride, magnesium chloride (d) Calcium chloride, magnesium chloride

Answer. (d)

 

Q. 28. A student while observing an embryo of a pea seed in the laboratory listed various parts of the embryo as given below:

On examining the list the teacher remarked that only three parts are correct.

Select three correct parts from the following list: 1

(a) Testa, Radicle, Cotyledon (b) Tegmen, Radicle, Micropyle

(c) Cotyledon, Plumule, Testa (d) Radicle, Cotyledon, Plumule

Answer. (d)

 

Q.29. If you are asked to select a group of two vegetables, out of the following, having homologous structures which one would you select?

(a) Carrot and radish (b) Potato and sweet potato

(c) Potato and tomato (d) Lady finger and potato

Answer. (a)

 

Q. 30. To determine the approximate value of the focal length of a given concave mirror, you focus the image of a distant object formed by the mirror on a screen. The image obtained on the screen, as compared to the object is always:

(a) Laterally inverted and diminished (b) Inverted and diminished

(c) Erect and diminished (d) Erect and highly diminished

Answer. (b)

 

Q. 31. Suppose you have focused on a screen the image of candle flame placed at the farthest end of the laboratory table using a convex lens. If your teacher suggests you to focus the parallel rays of the Sun, reaching your laboratory table, on the same screen, what you are expected to do is to move the:

(a) lens slightly towards the screen (b) lens slightly away from the screen

(c) lens slightly towards the Sun (d) lens and screen both towards the Sun

Answer. (a)

 

Q. 32. In your laboratory you trace the path of light rays through a glass slab for different values of angle of incidence (∠i) and in each case measure the values of the corresponding angle of refraction (∠r) and angle of emergence (∠e). On the basis of your observations your correct conclusion is:

(a) ∠i is more than ∠r, but nearly equal to Ze

(b) ∠i is less than ∠r, but nearly equal to ∠e

(c) ∠i is more than ∠e, but nearly equal to ∠r

(d) ∠i is less than ∠e, but nearly equal to ∠r

Answer. (a)

 

Q. 33. In the following ray diagram the correctly marked angles are:

(a) ∠i and ∠e (b) ∠A and ∠D

(c) ∠i, ∠e and ∠D (d) ∠r, ∠A and ∠D

Answer. (d)

 

Q. 34. A student adds a spoon full of powdered sodium hydrogen carbonate to a flask containing ethanoic acid. List two main observations, he must note in his note book, about the reaction that takes place. Also write chemical equation for the reaction.

Answer. When sodium hydrogen carbonate is added to a flask containing ethanoic acid, then

• brisk effervescence will be formed because of CO2 gas escaping from the reaction mixture.
• evolution of colourless and odourless gas. Some amount of heat is evolved during the reaction.
  

 

Q. 35. A student is observing a permanent slide showing sequentially the different stages of asexual reproduction taking place in yeast. Name this process and draw diagrams of what he observes in a proper sequence.

Answer. The process of reproduction in yeast is budding.

 

Q. 36. An object of height 2.5 cm is placed at a distance of 15 cm from the optical centre ‘O’ of a convex lens of focal length 10 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’, principal focus F and height of the image on the diagram.

Answer.

SET II

SECTION A

Q. 1. Write the name and structure of an alcohol with four carbon atoms in its molecule.

Answer. Name of an alcohol: Butanol

Q. 2. What are those organisms called which bear both the sex organs in the same individual? Give one example of such organism.

Answer. Organisms having both the sex organs in the same individual are called Hermaphrodite. Example, Earthworm.

 

Q. 3. Write one negative effect, on the environment, of affluent life style of few persons of a society.

Answer.

• Excessive use of air conditioners which is a part of affluent lifestyle emits a lot of heat in the atmosphere.
• Excessive use of packaging materials which are mostly made up of non- biodegradable material are not environment friendly.
• Excessive use of petrol in vehicles also causes pollution.
  Thus, affluent lifestyle results in the generation of excessive waste materials.

 

Q. 4. “The magnification produced by a spherical mirror is -3”. List four information’s you obtain from this statement about the mirror/image.

Answer. Magnification produced by a spherical mirror, m = -3

•  image is 3 times magnified than the object.
• image is inverted (as m has negative sign).
•  image is real.
• nature of the mirror is concave.

 

Q. 5. Forests are “biodiversity hot spots”. Justify this statement.

Answer. Forests are ‘biodiversity hot spots’. The measure of the biodiversity of an area is the number of species found there. Since in a forest there is a wide range of different life forms (bacteria, fungi, fern, flowering plants, nematodes, insects, birds, reptiles and so on) it can be termed a ‘biodiversity hotspot’. One of the main aims of conservation is to try and preserve the biodiversity we have inherited.

 

Q. 6. What is water harvesting? How can this technique help in the conservation of water?

Answer. Water harvesting is a conservation technique of capturing rain water when it falls and run off and taking measures to keep the water clean.

The main purpose of water harvesting is not to hold rain water on the surface of the earth but to make rain water percolate under the ground so as to recharge ‘groundwater’. This in turn reduces dependency on rainfall for irrigation.

 

Q. 7. On dropping a small piece of sodium in a test tube containing carbon compound ‘X’ , with molecular formula C2H6O, a brisk effervescence is observed and a gas ‘Y’ is produced. On bringing a burning splinter at the mouth of the test tube the gas evolved burns with a pop sound. Identify ‘X’ and ‘Y’. Also write the chemical equation for the reaction. Write the name and structure of the product formed, when you heat ‘X’ with excess cone, sulphuric acid.

Answer.

 

Q. 10. Three elements ‘X’, ‘Y’ and 71 have atomic numbers 7, 8 and 9 respectively.

(a) State their positions (Group number and period number both) in the Modern Periodic Table.

(b) Arrange these elements in the decreasing order of their atomic radii.

(c) Write the formula of the compound formed when ‘X’ combines with ‘Z’.

Answer.

 

Q. 12. In the context of reproduction of species state the main difference between fission and fragmentation. Also give one example of each.

Answer.

 

Q. 15. With the help of an example justify the following statement:

“A trait may be inherited, but may not be expressed.”

Answer. In Mendel’s experiment with pea plants, when he cross-bed a tall pea plant with a short plea plant, he found that the first generation (F1) was of only tall plants. In the F1 progeny, no short plants were obtained. Flow ever, in the F2 generation, both tall and short plants were obtained in the ratio 3 :1 respectively. In the F2 generation, both traits — tallness and shortness were inherited where the tall character was the dominant trait and short character was the recessive trait.

Conclusion. Reappearance of dwarf character in F2 generation proves that the dwarf trait was inherited but not expressed in the F2 generation.

 

Q. 16. The image of an object formed by a lens is of magnification -1. If the distance between the object and its image is 60 cm, what is the focal length of the lens? If the object is moved 20 cm towards the lens, where would the image be formed? State reason and also draw a ray diagram in support of your answer.

Answer.

 

Q. 19. (a) Define focal length of a spherical lens.

(b) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens? Find the size of the image also.

(c) Draw a ray diagram to show the formation of image in the above situation.

Answer.

SET III

SECTION A

Q. 1. Write the name and structure of an aldehyde with four carbon atoms in its molecule.

Answer. Name of an aldehyde : Butanal

Q. 2. List two functions of ovary of human female reproductive system.

Answer. Two functions of ovary:

1. To produce female gamete ovum.
2. To secrete female hormones estrogen and progestrone.

 

Q. 3. In a food chain of frog, grass, insect and snake, assign trophic level of frog.

Answer. Food chain. Grass —> insect —> frog —> snake

Frog belongs to 3rd trophic level.

 

Q. 4. The refractive indices of glass and water with respect to air are 3/2 and 4/3 respectively. If speed of light in glass is 2 x 108 m/s, find the speed of light in water.

Answer.

 

Q. 5. List four stakeholders which may be helpful in the conservation of forests.

Answer. Four stakeholders which may be helpful in the conservation of forests:

1. The people who live in and around the forest and are dependent to some extent on forest products for their live hood.
2. The forest department of the Government which owns the forest land and controls the resources from the forest.
3. The industrialists who use various forest products as raw materials for their factories.
4. The forest and wildlife activists who want to conserve the forests and see the forests in their original condition (pristine form).

 

Q. 6. The construction of large dams lead to social and environmental problems. List two problems of each category.

Answer. 

The construction of large dams leads to social and environmental problem.list two problem of each category

Social problem: Already poor tribals gets affected the most, loss of land, livelihood, home, property etc.

2. Not enough cash compensation offered by the government to the tribal groups, hence no source for balancing their livelihood.

Environmental problem: Ecosystem gets disturbed due to unannounced construction of dams.

2.Rate of deposition of sediments of sediments gets reduced and rate of erosion remains constant hence resulting in reduced water tables, less deposition of sediments in deltas etc

 

Q. 7. The position of eight elements in the Modern Periodic Table is given below where atomic numbers of elements are given in the parenthesis.

(i) Write the electronic configuration of Ca.

(ii) Predict the number of valence electrons in Rb.

(iii) What is the number of shells in Sr?

(iv) Predict whether K is a metal or a non-metal.

(u) Which one of these elements has the largest atom in size?

(vi) Arrange Be, Ca, Mg and Rb in the increasing order of the size of their respective atoms.

Answer.

 

Q. 8. Write three different chemical reactions showing the conversion of ethanoic acid to sodium ethanoate. Write a balanced chemical equation in each case. Write the name of the reactants and the products other than ethanoic acid and sodium ethanoate in each case.

Answer.

 

Q. 9. An element ‘X’ belongs to the 3rd period and group 13 of the Modern Periodic Table.

(a) Determine the valence electrons and the valency of ‘X’.

(b) Molecular formula of the compound formed when ‘X’ reacts with an element ‘Y’ (atomic number = 8).

(c) Write the name and formula of the compound formed when ‘X’ combines with chlorine.

Answer.

 

Q. 17. The image formed by a spherical mirror is real, inverted and is of magnification -2. If the image is at a distance of 30 cm from the mirror, where is the object placed? Find the focal length of the mirror. List two characteristics of the image formed if the object is moved 10 cm towards the mirror.

Answer.

 

Q. 24. (a) Define focal length of a divergent lens.

(b) A divergent lens of focal length 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use lens formula to determine the distance of the object from the lens and the size of the image formed.

(c) Draw a ray diagram to show the formation of image in the above situation.

Answer.

(a)

• The principal focus of a diverging lens is a point on its principal axis from which light rays, originally parallel to the axis appear to diverge after passing through the diverging (concave) lens.
•  The distance between pole and principal focus of a diverging lens is called the focal length. In the given diagram OF is the focal length.
  

Science

SET I

Section – A

Q 1.Write the molecular formula of the 2nd and the 3rd member of the homologous series whose first member is methane. 

Answer:

Ethane – C₂H₆

Propane – C₃H₈

 

Q 2.When a cell reproduces, what happens to its DNA? 

Answer:

During the process of reproduction, the transmission of DNA from parents to offspring takes place. Before reproduction, DNA is replicated, which means two copies of DNA are produced. When the cell divides, the two copies are distributed equally between the two daughter cells so that a similar amount and type of DNA is transferred from the parent cell to the daughter cells. It maintains the consistency in the amount and type of DNA in the living organism of a particular species.

 

Q 3. In the following food chain, 100J of energy is available to the lion. How much energy was available to the producer? 

Plant → Dear → Lion

Answer:

Plant → Dear → Lion

According to 10% law,

10% of x = 100

x = 1000 J in deer.

10% of y = 1000

y = 10,000 J in Plant.

 

Q 4. An object is placed at a distance of 30 cm from a concave lens of focal length 15 cm. List four characteristics (nature, position, etc.) of the image formed by the lens. 

Answer:

Given: u = -30 cm, f = -15 cm. (for concave lens)

We know that,

Characteristics of image:

• The image is formed at a distance of 10 cm from the concave lens on the left side.
• Image formed is virtual.
• Image formed is erect.
• The size of the image formed is diminished.

 

Q 5.State two advantages of conserving

(i) forests, and

(ii) wildlife. 

Answer:

(i) Advantages of conserving forest:

• It supports life, purifies air.
• Holds the soils and thus prevents the soil erosion.

(ii) Advantage of conserving wildlife:

• Balances ecology and biodiversity.
• Provides important things to sustain life.

 

Q 6. Explain two main advantages associated with water harvesting at the community level. 

Answer:

Two advantages associated with water harvesting at community level are:

• Water harvesting is an ideal solution to water problems in areas having inadequate water resources.
• It improves the quality of water and helps in raising the groundwater level.

 

Q 7. Write the structural formula of ethanol. What happens when it is heated with excess cones? H₂SO₄ at 443 K? Write the chemical equation for the reaction stating the role of cone. H₂SO₄ in this reaction. 

Answer:

Structural formula of ethanol is: CH₃CH₂OH

When ethanol is heated with excess of conc. H₂SO₄ at 443K it results in the dehydration of ethanol to give ethene.

Role of conc. H₂SO₄: Conc. H₂SO₄ acts as a dehydrating agent which removes water from the ethanol.

 

Q 8. Distinguish between esterification and saponification reaction with the help of the chemical equations for each. State one use of each (i) esters, and (ii) saponification process. 

Answer:

Esterification is opposite of saponification. In esterification:

RCOOH + R’OH → RCOOR’ + H2O

Whereas in saponification:

RCOOR’ + NaOH → RCOONa + R’OH

(i) Uses of Esters : Esters are used in making perfumes.

(ii) Uses of saponification reaction: Used in making soaps and soap products on a large scale.

 

Q 9. Write the number of periods and groups in the Modem Periodic Table. How does the metallic character of elements vary on moving

(i) from left to right in a period, and

(ii) down a group ? Give reason to justify your answer. 

Answer:

In the modem periodic table, there are 18 vertical columns known as Groups and 7 horizontal rows known as Periods.

Metallic character: It is defined as the tendency of an atom to lose electrons.

(i) Across the period i.e., from left to right, metallic character decreases.

(ii) Down the group i.e., from top to bottom, metallic character increases.

Reason: Across the period, the effective nuclear charge increases, thus decreasing its atomic radius. This favours the electronegativity and therefore the tendency ‘ to lose electrons is low. This accounts for the decrease in the metallic character. As we move down the group, the number of shells keep on increasing and therefore the atomic size increases and electronegativity decreases. This enhances the ability to lose electrons and therefore the metallic character increases.

 

Q 10. Na, Mg and Al are the elements of the 3rd period of the Modern Periodic Table having group number 1, 2 and 13 respectively. Which one of these elements has the (a) highest valency, (b) largest atomic radius, and (c) maximum chemical reactivity ? Justify your answer stating the reason for each. 

Answer:

Sodium (Na), At. number 11, 2, 8, 1

Magnesium (Mg), At. number 12, 2, 8, 2

Aluminium (Al), At. number 13, 2, 8, 3

(a) The element having the highest valency is Al, as it has 3 valence electrons.

(b) The element with the largest atomic radius is Na as left to right atomic radius decreases.

(c) The element with maximum chemical reactivity is Na as metallic character decreases left to right.

 

Q 11. Reproduction is one of the most important characteristics of living beings. Give three reasons in support of the statement. 

Answer:

Reproduction is an energy-consuming process which is not essential for the survival of an individual. But it is highly essential for all the living beings because of the following reasons:

• Reproduction helps in increasing the number of members of a population.
• By replacing the dead members with the new ones, it minimizes the risk of extinction of a species.
• It brings about variations in species, thus, leading to their evolution.

 

Q 12. What is vegetative propagation ? State two advantages and two disadvantages of this method. 

Answer:

Vegetative propagation is a mode of asexual reproduction in which new plants are obtained from vegetative parts of the plants such as shoots or stem for the propagation of new plants.

Two advantages of vegetative propagation are:

• Plants which do not produce seeds are propagated by this method.
• Vegetative propagation is a cheaper, easier and rapid method of propagation in plants than growing plants from their seeds. Plants grow very slowly and take 4 to 7 years to develop flowers when grown with their seeds.

Two disadvantages of vegetative propagation are:

• As there is no genetic variation, there is no chance of development of new and better varieties.
• The vegetatively propagated plants are more prone to diseases that are specific to the species.

 

Q 13. List three techniques that have been developed to prevent pregnancy. Which one of these techniques is not meant for males ? How does the use of these techniques have a direct impact on the health and prosperity of a family? 

Answer:

Three techniques that have been developed to prevent pregnancy are:

1. Mechanical Methods: Include condoms, diaphragm, IUCDs, etc.
2. Chemical Methods : Include oral contraceptive pills, spermicide.
3. Surgical Method: Includes vasectomy and tubectomy.
   The chemical methods are not meant for males.

The use of such contraceptive methods have various benefits, such as:

1. Large size of families have a negative impact on the economic status of the family.
2. Having pregnancies at quick successions reduces mother’s health and vitality. Use of contraceptive devices thus, effects the maternal health status.
3. Some contraceptive devices (such as condoms) are also helpful in preventing sexually transmitted diseases.

 

Q 14. How did Mendel explain.that it is possible that a trait is inherited but not expressed in an organism? 

Answer:

Some traits that are inherited may not express themselves. Such hidden traits are known as recessive traits. Mendel explained this phenomenon with the help of a monohybrid cross. In a monohybrid cross performed by Mendel, tall plant was crossed with a dwarf plant which produced all tall plants in F₁ progeny.

However, when these F₁ tall plants were crossed with each other, both tall and dwarf pea plants were obtained in F₂ generation. Reappearance of the dwarf pea plants in F₂ generation proves that the dwarf trait was inherited but not expressed in F₁ generation.

So, dwarfness traits of plants (pea plant) were not lost but are suppressed in the F₁ generation and thus reappears in F₂ generation.

 

Q 15. “Evolution and classification of organisms are interlinked”. Give reasons to justify this statement. 

Answer:

Classification refers to the grouping and naming of organisms based on the similarities and difference in their characters. Classification is done on the basis of ancestral characteristics and derived characteristics. So as we move from simple life forms to the complex organisms, we are actually tracing the path of evolution. All life forms on earth have progressively changed during evolution. So the hierarchy develops during classification which throws the light on the evolutionary relationship among organisms. Common ancestors can also be predicted with the help of classification.

 

Q 16. If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens is 10 D, what is its focal length in the Cartesian system ? 

Answer:

It is a concave lens (diverging lens).

 

Q 17. State the cause of dispersion of white light by a glass prism. How did Newton, using two identical glass prisms show that white light is made of seven colours ? Draw a ray diagram to show the path of a narrow beam of white light, through a combination of two identical prisms arranged together in inverted position with respect to each other, when it is allowed to fall obliquely on one of the faces of the first prism of the combination. 

Answer:

When a beam of white light enters a prism, it gets refracted at point and splits into its seven constituent colours. This splitting of the white light occurs because of different angles of bending for each colour and this different angles of bending occurs because different components of light have different refractive indices when passing through the glass prism.

Firstly, Newton made white light to fall on a prism, this cause dispersion of white light into seven colours. Newton then placed an inverted prism in the path of a colour band of seven colours. Only a beam of white ‘ light comes out from the second prism. So, Newton concluded that white light comprises of seven component colours.

 

Q 18. (a) Water is an elixir of life, a very important natural resource. Your science teacher wants you to prepare a plan for a formative assessment activity, “How to save water, the vital natural resource”. Write any two ways that you will suggest to bring awareness in your neighbourhood, on how to save water.

(b) Name and explain any one way by which the underground water table does not go down further. 

Answer:

(a) Water is one of the most precious natural resources that has varied importance in our lives. It is an essential component of the human body, and is used almost everywhere in our day to day activities such as cooking, washing, farming etc. It is an indispensable part of our lives, without which life on earth is not possible. However, the amount of freshwater available for sustaining life is very less, so it is very important to save water by the following ways:

• Turning off the taps during brushing, washing clothes/utensils etc., and use of buckets instead of showers for bathing.
• Reusing of water by storing water after washing fruits and vegetables for watering plants and cleaning cars.

(b) The underground water table can be recharged through rainwater harvesting. Rainwater harvesting is a process by which rain water is collected and stored for the purpose of recharging the ground water or for future use like for irrigation and agriculture. In India, rainwater harvesting is an old tradition which is followed till now in many parts of India. For example, bawris are traditional architectural rainwater harvesters that were built for collecting water in the state of Rajasthan.

There are two ways of rainwater harvesting:

• Surface runoff harvesting: In urban areas, rainwater that flows away from the surface can be collected and used for various purposes.
• Rooftop rainwater harvesting: The rainwater on the roofs of the buildings is collected through canals that drains the water into ground reservoirs. This stored water is later utilised.

 

Q 19. Why are certain compounds called hydrocarbons? Write the general formula for homologous series of alkanes, alkenes and alkynes and also draw the structure of the first member of each series. Write the name of the reaction that converts alkenes into alkanes and also write a chemical equation to show the necessary conditions for the reaction to occur. 

Answer:

Compounds consisting of carbon and hydrogen are known as hydrocarbons.

1. Saturated hydrocarbons: Alkanes (C_nH_2n+2) are the compounds of carbon which have single bond.

2. Unsaturated hydrocarbons: The compounds of carbon having double bonds are alkene (C_nH_2n) and those having triple bonds are alkyne (C_nH_2n-2).

The reaction which converts unsaturated hydrocarbons to saturated hydrocarbons i.e., alkenes to alkane is known as hydrogenation reaction. It is used to obtain ghee from oil.

 

Q 20. (a) Write the functions of each of the following parts in a human female reproductive system:

(i) Ovary

(ii) Uterus

(iii) Fallopian tube

(b) Write the structure and functions of the placenta in a human female. 

Answer:

(a) (i) Functions of the Ovary:

• It produces female gametes (ova).
• It secretes female sex hormones

(ii) Functions of Uterus:

• It supports and nourishes the developing foetus.
• It expands according to the growth of the baby.

(iii) Functions of Fallopian tubes:

• They carry eggs from the ovary to the uterus.
• They act as the site for fertilisation.

(b) The placenta is the connecting link between the mother’s body and the baby. It is a disc embedded in the uterine wall. This special tissue contains villi on the embryo’s side of the tissue. The mother’s end of the placenta has blood spaces, which surrounds the villi. Placenta functions as a site of exchange of materials between the blood of the mother to the baby. The developing embryo generates certain waste substances that are also removed through placenta. Thus, the placenta serves as the nutritive, respiratory and excretory organ of the foetus.

 

Q 21. With the help of one example for each, distinguish between the acquired traits and the inherited traits. Why are the traits/ experiences acquired during the entire lifetime of an individual not inherited in the next generation? Explain the reason for this fact with an example. 

Answer:

S.No.	Acquired traits	Inherited traits
1.	Those traits that are developed by the individual during his lifetime.	Those traits which are present in an in­dividual since birth.
2.	They are a result of changes in non-reproductive issues.	They are a result of changes in the DNA.
3.	They cannot be passed on to the progeny,       e.g., pierced ear, large muscle size etc.	They are transmit­ted in the progeny, e.g., colour of eyes, skin or hair.

Traits can be passed on to the next generation only when they have some direct effect on the genes. The traits acquired during the lifetime of an individual cannot be inherited as they do not affect the genetic makeup of an organism. In fact, these traits develop due to the use and disuse of organs or due to the direct effect of the environment. Thus, they are not passed on to the next generation. For example, a wrestler develops large muscles because of his training programme, it does not mean that his offspring will necessarily have large muscles. Similarly, if a lady pierces her nose, the children produced to her will not have pierced nose by birth.

 

Q 22. Analyse the following observation table showing a variation of image-distance (v) with object-distance (u) in case of a convex lens and answer the questions that follow without doing any calculations:

S.No.	Object-Distance u (cm)	Image-Distance v (cm)
1.	-100	+ 25
2.	-60	+ 30
3.	-40	+ 40
4.	-30	+ 60
5.	-25	+ 100
6.	-15	+ 120

(a) What is the focal length of the convex lens ? Give a reason to justify your answer.

(b) Write the serial number of the observation which is not correct. On what basis have you arrived at this conclusion?

(c) Select an appropriate scale and draw a ray diagram for the observation at S. No. 2. Also, find the approximate value of magnification. 

Answer:

(a) From observation 3, the radius of curvature of the lens is 40 cm as distance of object and the distance of the image is the same.

Focal length, f = R/2 = 40/2 = 20 cm.

(b) S. No. 6 is not correct, as for this observation the object distance is between focus and pole and in such cases, the image formed is always virtual, but in this case real image is forming as the image distance is positive, hence, v should be negative

 

Q 23. (a) If the image formed by a mirror for all positions of the object placed in front of it is always diminished, erect and virtual, state the type of the mirror and also draw a ray diagram to justify your answer. Write one use such mirrors are put to and why.

(b) Define the radius of curvature of spherical mirrors. Find the nature and focal length of a spherical mirror whose radius of curvature is + 24 cm. 

Answer:

(a) The type of the mirror is a convex mirror. (diverging mirror)

The ray diagram is shown below:

Use of convex mirror: Convex mirror is used as rearview mirror in vehicles as it always produces a virtual, erect and diminished image of an object. So, images of vehicles over a wide area can be seen easily in it.

(b) Radius of curvature: The distance between the centre of curvature and pole of a spherical mirror is called radius of curvature.

R = +24 cm

f = R/2 = 24/2 = +12 cm

The mirror is convex mirror.

 

Q 24. (a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain

(i) Why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.

(ii) The type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.

(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention. 

Answer:

(a) Two possible reasons due to which this defect of vision may have arisen are:

1. Increase in curvature of the lens.

2. Elongation of the eyeball.

(i) A myopic eye has its far point nearer than infinity. It forms the image of a distant object in front of the retina as shown below:

Image is formed in front of Retina

In the given case, student’s far point is 5 m. So, image of the object placed beyond 5 m from his eyes is formed in front of the retina and object appears blurred. That is why the student is unable to see distinctly the objects placed beyond 5 m from his eye.

(ii) Since a concave lens has an ability to diverge the incoming rays. Therefore, it is used to correct this defect of vision. The image is formed at the retina by the use of a concave lens of suitable power as shown.

Section – B

Q 25. When you add a few drops of acetic acid to a test-tube containing sodium bicarbonate powder, which one of the following is your observation? 

(a) No reaction takes place.

(b) A colourless gas with the pungent smell is released with brisk effervescence.

(c) A brown coloured gas is released with brisk effervescence.

(d) Formation of bubbles of a colourless and odourless gas.

(d) Formation of bubbles of a colourless and odourless gas. 

 

Q 26. While studying the saponification reaction, what do you observe when you mix an equal amount of colourless vegetable oil and 20% aqueous solution of NaOH in a beaker? 

(a) The colour of the mixture has become dark brown.

(b) A brisk effervescence is taking place in the beaker.

(c) The outer surface of the beaker has become hot.

(d) The outer surface of the beaker has become cold.

Answer:

(c) The outer surface of the beaker has become hot.

 

Q 27. A student requires hard water for an experiment in his laboratory which is not available in the neighbouring area. In the laboratory, there are some salts, which when dissolved in distilled water can convert it into hard water. Select from the following groups of salts, a group, each salt of which when dissolved in distilled water will make it hard. 

(a) Sodium chloride, Potassium chloride

(b) Sodium sulphate, Potassium sulphate

(c) Sodium sulphate, Calcium sulphate

(d) Calcium sulphate, Calcium chloride

Answer:

(d) Calcium sulphate, Calcium chloride

 

Q 28. To perform an experiment to identify the different parts of an embryo of a dicot seed, first of all you require a dicot seed. Select dicot seeds from the following group. 

Wheat, Gram, Maize, Pea, Barley, Groundnut

(a) Wheat, Gram and Pea

(b) Gram, Pea and Ground-nut

(c) Maize, Pea and Barley

(d) Gram, Maize and Ground-nut

Answer:

(b) Gram, Pea and Ground-nut

 

Q 29. The following vegetables are kept in a basket:

Potato, Tomato, Radish, Brinjal, Carrot, Bottle-gourd

Which two of these vegetables correctly represent the homologous structures? 

(a) Carrot and Tomato

(b) Potato and Brinjal

(c) Radish and Carrot

(d) Radish and Bottle-gourd

Answer:

(c) Radish and Carrot

 

Q 30. Study the given ray diagrams and select the correct statement from the following: 

(a) Device X is a concave mirror and device Y is a convex lens, whose focal lengths are 20 cm and 25 cm respectively.

(b) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 10 cm and 25 cm respectively.

(c) Device X is a concave lens and device Y is a convex mirror, whose focal lengths are 20 cm and 25 cm respectively.

(d) Device X is a convex lens arid device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.

Answer:

(d) Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.

 

Q 31. A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens. 

(a) away from the screen

(b) towards the screen

(c) to a position very far away from the screen.

(d) either towards or away from the screen depending upon the position of the object.

Answer:

(d) either towards or away from the screen depending upon the position of the object.

 

Q 32. A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence (∠i). He then measures the corresponding values of the angle of refraction (∠r) and the angle of emergence (∠e) for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be: 

(a) ∠i > ∠r > ∠e

(b) ∠i = ∠e > ∠r

(c) ∠i < ∠r < ∠e

(d) ∠i = ∠e < ∠r

Answer:

(b) ∠i = ∠e > ∠r

 

Q 33. Study the following ray diagram

In this diagram, the angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by 

(a) y, p, z

(b) x, q, z

(c) p, y, z

(d) p, z, y

Answer:

(c) p, y, z

 

Q 34. Mention the essential material (chemicals) to prepare soap in the laboratory. Describe in brief the test of determining the nature (acidic/alkaline) of the reaction mixture of saponification reaction. 

Answer:

The essential chemicals required to prepare soap in the laboratory are oil and sodium hydroxide solutions. In order to determine the nature of the reaction mixture of saponification reaction, we dip red litmus paper into it which will turn blue after a while indicating that it is a basic mixture.

 

Q 35. Draw in sequence (showing the four stages), the process of binary fission in Amoeba. 

Answer:

Binary Fission in Amoeba is the asexual type of reproduction in which the organism splits directly into two equal¬sized offsprings, each with a copy of the parent’s genetic material.

 

Q 36. A student focuses the image of a candle flame, placed at about 2 m from a convex lens of focal length 10 cm, on a screen. After that, he moves gradually the flame towards the lens and each time focuses its image on the screen. 

1. In which direction does he move the lens to focus the flame on the screen?
2. What happens to the size of the image of the flame formed on the screen?
3. What difference is seen in the intensity (brightness) of the image of the flame on the screen?
4. What is seen on the screen when the flame is very close (at about 5 cm) to the lens?

Answer:

1. He moves the lens away from the screen to focus on the image.
2. Size of the image increases.
3. The intensity of the image decreases as the flame moves towards the lens.
4. Nothing can be seen as the image formed is virtual.

SET II

Q 1. Write the molecular formula of the 2nd and 3rd member of the homologous series whose first member is ethene. 

Answer:

1. Propene: C₃H₆

2. Butene: C₄H₈

 

Q 2. Newly formed DNA copies may not be identical at times. Give one reason. 

Answer:

During the process of replication of DNA, most of the base sequences in the new copies are identical to those in the parent DNA. However, some changes can occur either due to mutation or due to minor errors during the replication process. Thus, the newly formed DNA copies may not be identical at times.

 

Q 3.In the following food chain, plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes?

Plants → Rats → Snakes → Hawks 

Answer:

500 J of energy is available to the rats thus according to 10% law, 50 J energy will be available to snakes and 5 J energy will be available to hawk.

 

Q 4. An object is placed at a distance of 15 cm from a convex lens of focal length 20 cm. List four characteristics (nature, position, etc.) of the image formed by the lens. 

Answer:

Given, u = -15 cm, f = 20 cm

1/f = 1/v – 1/u

1/20 = 1/v + 1/15

1/v = 1/20 – 1/15

v = -60 cm

Four characteristics of the image formed by the lens are:

• Virtual
• Erect
• At a distance of 60 cm on the same side of the lens as the object
• Enlarged or magnified image.

 

Q 5.Why is an equitable distribution of resources essential in a society? List two forces which are against such distribution. 

Answer:

Equitable distribution of resources is when every individual gets an equal right to access all the available resources and is benefited directly or indirectly. It also avoids the division of society to an extent.

The main forces which work against equitable distribution:

• Lack of natural resources.
• Excessive consumption by the rich.
• Profit motive of people exploiting resources.
• Corruption. (Any two)

 

Q 6. Why must we conserve our forests? List two factors responsible for causing deforestation. 

Answer:

We must conserve forests because we derive countless benefits such as food, timber etc. from them and they are an important component of our ecosystem. Factors that contribute to deforestation are as follows:

1. Large scale development projects have contributed to the loss of forests.
2. Forests are cleared on a large scale to meet the growing needs of industrialisation, especially fuelwood and for other forest products and minerals.
3. Mining has also contributed to deforestation.
4. With the increase in population and growing demand for commercial crops and the need for more and more land for agriculture, has to lead to deforestation.
5. Growing urbanisation, trees are cut to establish cities, to lay down infrastructure.

 

Q 9. What happens when (write a chemical equation in each case)

(a) ethanol is burnt in the air?

(b) ethanol is heated with an excess cone. H2SO4 at 443 K?

(c) a piece of sodium is dropped into ethanol? 

Answer:

 

Q 10. Explain an esterification reaction with the help of a chemical equation. Describe an activity to show esterification. 

Answer:

The reaction of carboxylic acid with alcohol forms an ester. This process of formation of ester is called esterification.

CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O

Activity:

1. Take 1 ml of ethanol and 1 ml of glacial acetic acid in a boiling tube and mix the contents well.
2. Add a few drops of conc. H₂SO₄ to it.
3. Warm the contents on a water bath for a few minutes.
4. Now pour the solution in a beaker containing 20-50 mL of water.
5. A sweet fruity smell indicating the formation of an ester is observed.

 

Q 11. With the help of two suitable examples, explain why certain experiences and traits earned by people during their lifetime are not passed on to their next generations. When can such traits be passed on? 

Answer:

The experiences and qualifications that a person earns during their lifetime are examples of acquired traits. These traits are not inherited, they do riot affect the genetic makeup. They are developed due to the direct affect of the environment. Thus they are not passed to the next generation. Piercing of ears or large sized muscles of the wrestler are not carried by the next generation. Traits can only be passed on to the next generation only when they have some direct effect on the genes. For example, mutation is caused in the germ cells of a person due to exposure to some harmful radiations, it is likely that the mutation will be passed on to the subsequent generations.

 

Q 14. Describe reproduction by spores in Rhizopus. 

Answer:

Rhizopus is a fungus that reproduces by spore formation. The fungal hyphae gives rise to a globular structure known as sporangium. The sporangium gives rise to several spores by repetitive division of its nucleus. Each nucleus gets surrounded by a part of cytoplasm and thus develops into a spore. These spores then mature inside the sporangium. Once they are fully mature, the sporangium bursts to release these spores in the environment. Since the spores disperse through air, they can land on various sites. These sites may be favourable or unfavourable. During unfavourable conditions, these spores are protected by a tough coat. Once favourable conditions return, they germinate and grow into new hyphae.

 

Q 16. Draw ray diagrams to show the formation of three times magnified (a) real, and (b) virtual image of an object by a converging lens. Mark the positions of O, F and 2F in each diagram. 

Answer:

(a) For real image: To get a three-times magnified image, the object is placed between F1 & 2F1

(b) For virtual image: To get a three-times magnified image, the object is placed between the F1 and optical centre O.

 

Q 17. What is the dispersion of white light? State its cause. Draw a ray diagram to show the dispersion of white light by a glass prism. 

Answer:

The phenomenon of splitting of white light into its seven constituent colours, when it passes through a glass prism, is called the dispersion of light.

When a beam of white light enters a prism, it gets refracted at point and splits into its seven constituent colours i.e.r violet, indigo, blue, green, yellow, orange and red i.e., VIBGYOR. This splitting of light rays occurs because of the different angles of bending for each colour and this different angles of bending occurs because different components of light have different refractive indices or speed of different colours is different in glass when passing through the glass prism. When a beam of sunlight is allowed to fall on one of the rectangular surfaces of the glass prism, we obtain a coloured spectrum with red and violet colour at its extremes.

SET III

Q 1. Write the molecular formula of the 2nd and 3rd member of the homologous series where the first member is ethyne. 

Answer:

1. CH₃C = CH (propyne), n = 3

2. CH₃CH₂C = CH (Butyne), n = 4

 

Q 2.Why is variation important for a species? 

Answer:

Variation is necessary for the survival of species as variation makes species more adapted to survive with the change environmental conditions. The vari? t species are more adapted to changing the environment. Therefore, they can survive better and reproduce to pass the genes to the offsprings.

 

Q 3. In the following food chain, 20,000 J of energy was available to the plants. How much energy would be available to man in this chain?

Plants → Sheep → Man 

Answer:

In the given food chain, according to 10% law,

Plants(20,000J) → Sheep(2000J) → Man(200J)

Amount of energy available to the man is 200 J.

 

Q 5. You being an environmentalist are interested in contributing to the conservation of natural resources. List four activities that you can do on your own. 

Answer:

We can bring the following activities in practice to conserve the natural resources:

1. We can reuse and recycle the paper products so that cutting of trees could be reduced.
2. We can reduce the consumption of water by avoiding its wastage in our day to day activities.
3. We can also adopt water harvesting like rainwater harvesting.
4. We can reduce the consumption of fossil fuels by using public transport, carpool and switching off vehicles at signals.

 

Q 6. Why are coal and petroleum categorised as natural resources ? Give a reason as to why they should be used judiciously. 

Answer:

Natural resources are those living and non-living sources available in our environment which are exploited to meet the human requirements. Since coal and petroleum are actually the fossils of the dead plants and animals respectively, hence considered as natural resources.

Both coal and petroleum are used as important sources of energy since long time. Both these fossil fuels were formed millions of years ago from the degradation of biomass. Since these fossil fuels are non-renewable in nature and they have limited reserves, therefore they must be used judiciously, otherwise they will get exhausted very soon.

 

Q 9. What is periodicity in properties of elements with reference to the Modem Periodic Table? Why do all the elements of the same group have similar properties? How does the tendency of elements to gain electrons change as we move from left to right in a period ? State the reason of this change. 

Answer:

The occurrence of the elements with similar properties after certain regular intervals when they are arranged in increasing order of atomic number is called periodicity. The periodic repetition of the properties is due to the recurrence of similar valence shell configuration after regular interval.

The elements in a group have same valence electrons thus similar chemical properties. In a period, the tendency to gain electrons increases from left to right. This tendency increases because the hold of the nucleus on the outermost electrons becomes weak thus it becomes easy to eject the electron.

 

Q 10. Write the electronic configuration of two elements X and Y whose atomic numbers are 20 and 17 respectively. Write the molecular formula of the compound formed when element X reacts with element Y. Draw the electron-dot structure of the product and also state the nature of the bond formed between both the elements. 

Answer:

X = 20; 2, 8, 8, 2

Y = 17; 2, 8, 7

The nature of the bond will be ionic.

 

Q 12. What is an organic evolution ? It cannot be equated with progress. Explain with the help of a suitable example. 

Answer:

Organic evolution refers to the gradual changes that occur in living organisms over time. It is the result of change in the genetic makeup of the organism due to mutation and other sources of variations. „ The favourable mutations are accepted by nature and provide the organism an adaptive advantage, leading to its evolution. Evolution cannot always be equated to progress because it does not always lead to the formation of a new species. In fact, most of the time, it leads to the generation of diversity. One species does not necessarily get eliminated to give rise to new ones in prevailing environments. Also, the newly formed species may have complex organisations because of evolution but it cannot be considered better than the earlier species. Many older and simpler designs still survive in nature. For example, bacteria are one of the simplest life forms on earth and still they can survive in the most adverse conditions, such as hot springs, deep sea thermal vents etc. Therefore, having more complex body designs does not make any species superior to others.

 

Q 13. List the two types of reproduction. Which one of the two is responsible for bringing in more variations in its progeny and how? 

Answer:

Reproduction methods are of two types: Sexual and Asexual. Out of these, sexual reproduction brings more variation in organisms. In sexual reproduction fusion of male and female gametes from different organisms occurs. Since the fusion of gametes come from two different individuals, the offspring exhibit more diversity of characters. Also during gamete formation, meiosis occurs which brings new combinations of genes. Both these factors lead to more variations in the progeny.

 

Q 16. “A lens can form a magnified erect image as well as magnified inverted image of an object placed in front of it.” State the nature of this lens and draw ray diagrams to justify the above statement. Mark the positions of O, F and 2F in the diagram.

Answer:

Convex/Converging lens.

Two ray diagrams are drawn to show it-

(a) When object is placed between O and F1, the image formed is magnified, Virtual and erect.

(b) When object is placed between F and 2F, the image formed is magnified and inverted.

Q 17. What is “dispersion of white light”? Draw a labelled diagram to illustrate the recombination of the spectrum of white light. Why is it essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other? 

Answer:

The phenomenon of splitting of white light into its constituent colours on passing through a prism is known as the dispersion of white light. This splitting of the light rays occurs because of the different angles of bending for each colour and this different angles of bending occurs because different component of light faces different refractive index (or speed of different colours is different) when passing through the glass prism.

It is essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other so that the second prism completely nullifies the dispersion caused by the first prism and we get pure white light.