Category: Class 10

Science

Section – A

Q.1. Name two industries based on forest produce. 

Answer: Timber industries and paper manufacturing industries are based on forest produce. 

Q.2. Why are the heating elements of electric toasters and electric irons made of an alloy rather than a pure metal? 

Answer: The resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (bum) readily at higher temperatures. Therefore, conductors of electric heating devices, such as toasters and electric irons, are made up of an alloy rather than pure metal. 

Section – B 

Q.3. Write the molecular formula of ethene and draw its electron dot structure. Answer: The molecular formula of ethene is C₂H₄ 

Electron dot structure of ethene. 

Q.4. Given reasons: 

(a) Platinum, gold and silver are used to make jewellery. 

(b) Metals like sodium and potassium are stored under oil. 

OR

Q.4. Silver articles become black when kept in open for some time, whereas copper vessels lose their shiny brown surfaces and gain a green coat when kept in open. Name the substances present in air with which these metals react and write the name of the products formed. 

Answer: (a) Platinum, gold and silver are used to make jewellery because of its bright and shiny surface. This property is called metallic lustre. 

(b) Metals like sodium and potassium are stored under oil because they are very reactive in nature, they react with oxygen present in air. Thus to prevent their oxidation they are kept in the oil. 

OR

Answer: Silver articles become black when kept in open for some time, whereas copper vessel lose their shiny brown surfaces and gain a green coat when kept in open because silver articles reacts with sulphur compounds such as hydrogen sulphide present in the air to form silver sulphide (Ag₂S) whereas copper reacts slowly with CO₂ and water present in the air to form green coating of mixture of copper carbonate and copper hydroxide. 

Q.5. The absolute refractive index of Ruby is 1.7. Find the speed of light in Ruby. The speed of light in a vacuum is 3 x 10⁸ m/s. 

Answer: We know that, 

Refractive index of ruby 

Section – C 

Q.6. On heating blue coloured powder of copper (II) nitrate in a boiling tube, black copper oxide, O₂ and a brown gas X is formed. 

(a) Identify the type of reaction and gas X

(b) Write the balanced chemical equation of the reaction. 

(C) Write the pH range of aqueous solution of the gas X. 

Answer: 

(a) Decomposition reaction 

The gas X is Nitrogen dioxide (NO₂) 

(c) Oxides of non-metals are acidic. Therefore the aqueous solution of this gas would be acidic. 

The pH would be less than 7.

Q.7. (a) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid? 

(b) Dry hydrogen chloride gas does not change the colour of dry litmus paper why? 

OR

Q.7. How is sodium hydroxide manufactured in industries? Name the process. In this process, a gas X is formed as a byproduct. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reaction involved. 

Answer: (a) The process of mixing concentrated acid with water is highly exothermic. So, when a concentrated acid is added to water then heat is easily absorbed by a large amount of water. Thus it is recommended to add acid to water and not water to the acid. 

(b) Dry hydrogen chloride does not contain any hydrogen ions in it, so it does not show acidic behaviour and thus does not change the colour of dry litmus paper. 

OR

Answer: Sodium hydroxide is manufactured by the electrolysis of a concentrated aqueous solution of sodium chloride 

The process of manufacture of sodium hydroxide by electrolysis process is called the chloralkali process. Gas X is chlorine gas and compound Y is calcium oxychloride (Bleaching powder) 

Q.8. What are amphoteric oxides? Give an example. 

Write balanced chemical equations to justify your answer. 

Answer: Those oxides which behave both acidic and basic oxides are called amphoteric oxides. Example: Al₂O₃ (Alumina) 

Q.9. What is a homologous series of carbon compounds ? Give an example and list its three characteristics. 

Answer: A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH₂ group. Example: Alkanes with general formula C_nH_2n+2 Characteristics: 

• All the members of a homologous series can be represented by the same general formula. 

• Any two adjacent homologues differ by 1 carbon atom and 2 hydrogen atoms in their molecular formulae. 

• The difference in the molecular masses of any two adjacent homologues is 14 u. 

Q.10. List in tabular form three distinguishing features between autotrophic nutrition and heterotrophic nutrition. 

Answer: 

Q.11. What is transpiration? List its two functions. 

OR

Q.11. (a) What is translocation? Why is it essential for plants? 

(b) Where do the substances in plants reach as a result of translocation?

Answer: The evaporation of water from the leaves of a plant is called transpiration. Functions of transpiration 

1. It helps in the upward movement of water and minerals from the root to the leaves through the stem. 

2. Helps in cooling the plant surface. 

OR

Answer: (a) The transport of food from leaves to other parts of the plant is called translocation. Translocation is essential for plants because without it food prepared by the leaves cannot reach other parts of the plant for their growth and development. 

(b) The substances in plants reach other tissues in plants from the leaves as a result of translocation. 

Q.12. What is carpel? Write the function of its various parts. 

Answer: The flask-shaped organ in the centre of a flower is called carpel. It is also called a female reproductive organ of the plant. It is made up of three parts: 

1. Stigma 

2. Style 

3. Ovary 

1. Stigma is the top part of carpel and is sticky. So, it receives the pollen from the anther of stamen.

2. Style connects stigma to ovary. 

3. Ovary contains female gametes of the plant and helps in reproduction. 

Q.13. A student holding a mirror in his hand directed the reflecting surface of the mirror towards the Sun. He then directed the reflected light on to a sheet of paper held close to the mirror. 

(a) What should he do to bum the paper? 

(b) Which type of mirror does he have? 

(c) Will he be able to determine the approximate value of the focal length of this mirror from this activity ? Give reason and draw ray diagram to justify your answer in this case. 

OR

Q.13. A 10 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 12 cm. The distance of the object from the lens is 18 cm. Find the nature, position and size of the image formed.

Answer: (a) He should place the sheet of paper at the focus of the mirror to burn the paper. 

(b) He has a concave mirror. 

(c) Yes, the sheet of paper will start burning at the focus of the mirror which will give an approximate value of focal length, i.e., the distance between the mirror and the point where the sheet of paper starts burning. 

OR

Answer: A concave mirror forms a real image of the sun, 

Given: Height of object, h₁ = +10 cm. Focal length, f = +12 cm. 

Object distance, u = -18 cm. From the lens formula, 

The position of image formed is at distance of 36 cm from convex lens. Since the value of the magnification is more than 1 (it is 2), the image formed is larger than object. The minus sign of magnification shows that image is formed below the principal axis. Hence, the image formed is real and inverted, 

Q.14. What are solar cells? Explain the structure of solar panel. List two principal advantages associated with solar cells. 

Answer: Solar cells are the devices which convert solar energy into electricity. A simple solar cell is made up of a sandwich of a silicon-boron layer and a silicon-arsenic layer. Boron and arsenic are present in a very small amount. A piece of wire is soldered into the top of the upper layer of cell and another piece of wire is soldered at the bottom of the lower layer to pass on the current. The solar cell is covered with a glass cover for protection. Advantages: 

• Solar cells have no moving parts. 

• It requires no maintenance. 

Q.15. Write the essential function performed by ozone at the higher levels of the Earth’s atmosphere? How is it produced ? Name the synthetic chemicals mainly responsible for the drop of amount of ozone in the atmosphere. How can the use of these chemicals be reduced?

Answer: Ozone layer absorbs most of the harmful ultraviolet radiations from the sun to the earth. It is formed high up in the atmosphere by the action of ultraviolet radiation on oxygen gas. Chlorofluorocarbons are the synthetic chemicals responsible for the drop of amount of ozone in the atmosphere. 

The use of these chemicals can be reduced by: 

• Replacement of chlorofluorocarbons with hydrochlorofluorocarbons because it breaks down more quickly. 

• Safe disposal of old appliances such as refrigerators and freezers. 

Section – D 

Q.16. (a) List any three observations which posed a challenge to Mendeleev’s Periodic law. 

(b) How does the metallic character of elements vary on moving (i)from  left to right in a period, (ii) from top to bottom in a group of the Modem Periodic Table? Give a reason for your answer. 

OR

Q.16. The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1,3,5 and 7, electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modem Periodic Table. Write the electronic configuration of the atoms of B and D, and the molecular formula of the compound formed when B and D combine. 

Answer: (a) Three observations which posed a challenge to Mendeleev’s Periodic law are: 

• The position of isotopes could not be explained. 

• Wrong order of atomic masses of some elements could not be explained. 

• A correct position could not be assigned to hydrogen in the periodic table. 

(b) (i) On moving from left to right in a , period, the metallic character of elements decreases because electropositive character decreases. 

(ii) Ongoing down in a group of the periodic table, the metallic character of elements increases because of electropostive character of elements increases. 

OR

Answer: A – 1st group 

B – 13th group 

C- 15th group 

D – 17th group 

Electronic configuration B – Atomic number = 13. KLM 283 D – Atomic number = 17 

KLM 287 The molecular formula of the compound when B and D combine is BD 

Q.17. (a) Why is the use of iodised salt advisable? Name the disease caused due to deficiency of iodine in our diet and state its one symptom. 

(b) How do nerve impulses travel in the body? Explain. 

OR

Q.17. What is hydrotropism? Design an experiment to demonstrate this phenomenon. 

Answer: (a) lodised salt is advisable because iodine is necessary for the formation of thyroxine hormone by the thyroid gland Goitre is the disease caused due to its deficiency. Symptom: The neck of the person appears to be swollen due to the enlargement of thyroid gland. 

(b) Two neurons are not joined to one another completely. There is a small gap between a pair of neuron. This gap is called synapse. The nerve impulse are carried out to this gap by the help of neurotransmitter (chemical substance). The conduction of nerve impulse through the synapse takes place in the form of electrical nerve impulse. When a stimulus acts on the receptor an electrical impulse is produced with the help of chemical reaction. This electrical impulse passes through the synapse and then to the other neuron. Thus, in this way nerve impulses travel in the body.

OR

Answer: The movement of root of plants towards water is called hydrotropism. Take two glass troughs A and B fill each one of them two-thirds with soil. In trough A plant a tiny seedling figure 

(a). In trough B plant a similar seedling and also place a small clay pot inside the soil figure 

(b). Water the soil in trough A daily and uniformly. Do not water the soil in trough B but put some water in the clay pot buried in the soil. Leave both the troughs for a few days. 

Now, dig up the seedlings carefully from both the trough without damaging their roots. We will find that the root of seedling in through A is straight. On the other hand, the root of seedling in trough B is found to be bent to the right side (towards the clay pot containing water) figure (b). This can be explained as follows. 

In through A, the root of seedling gets water from both sides (because the soil is watered uniformly) in trough B, the roots gets water oozing out from the clay pot which is kept on the right side. So, the root of seedling in trough B grows and bends towards the source of water to the right side. The experiment shows that the root of a plant grows towards water. In other words, the root of a plant is positively hydrotropic. 

Q.18. (a) What are homologous structures ? Give an example. (b) “The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it.” justify this statement with the help of a flow chart showing sex-determination in human beings. 

Answer: (a) The structures which have the same basic design but different functions are called homologous structures or homologous organs. Example: Forelimbs of a man, a lizard, a frog they have same basic design of bones but perform different functions. (b) The sex of a newborn depends on what happens at the time of fertilization. 

1. If a sperm carrying X chromosome fertilizes the ovum carrying X chromosome, then the girl child will be born and the child will have XX combination of sex chromosomes. 

2. If a sperm carrying Y chromosome fertilizes the ovum carrying X chromosome, then the child born will be.

The above presentation clearly shows that it is matter of chance whether the newborn will be boy or girl and none of the parents may be considered responsible for it.

Q.19. When do we consider a person to be myopic or hypermetropic ? List two causes of -hypermetropia. Explain using ray diagrams how the defect associated with hypermetropic eye can be corrected. 

Answer: Myopia is the defect in vision in which a person cannot see the distant objects clearly whereas in hypermetropia is the defect in which a person cannot see nearby objects clearly. Hypermetropia is caused due to: 

1. Decrease in converging power of eye-lens. 

2. Too short eye ball. 

In a hypermetropic eye, the image of near by object lying at normal near point N (at 25 cm) is formed behind the retina. 

Hypermetropic eye can be corrected using convex lenses. When a convex lens of suitable power is placed in front of hypermetropic eye, then the diverging rays of light from the object are converged first by the convex lens used. This form a virtual image of the object at another near point N’. Now, the rays can be easily focused by the eye lens to form an image on retina. 

Q.20. (a) How will you infer with the help of an experiment that the same current flows through every part of a circuit containing three resistors in series connected to a battery? 

(b) Consider the given circuit and find the current flowing in the circuit and potential difference across the 150 resistor when the circuit is closed. 

OR

Q.20. (a) Three resistors R1, R2 and Rg are connected in parallel and the combination is connected to a battery, ammeter, voltmeter and key. 

Draw suitable circuit diagram and obtain an expression for the equivalent resistance of the combination of the resistors. 

(b) Calculate the equivalent resistance of the following network.

Answer: (a) Let three resistors R1, R2 and R3 are connected in series which are also connected with a battery, an ammeter and a key as shown in figure 

When key is closed, the current starts flowing through the circuit. Take the reading of ammeter. Now change the position of ammeter to anywhere in between the resistors and take its reading. We will observe that in both the cases reading of ammeter will be same showing same current flows through every part of the circuit above. 

(b) Given R1 = 50, R2 = 100, R3 = 150, V = 30 V 

Total resistance, R = R₁ + R₂ + R₃ [∵ 5, 10 and 15 are connected in series]

 = 5 + 10 + 15 

= 30

Potential difference, V = 30 V 

Current in the circuit, I = ?

From Ohm’s law.

IR = 30 = 1 A 

Current flowing in the circut = 1A 

Potential difference across 15 resistors = 1R3 = 1 x 15 = 15 V .

OR

Answer: (a) Let R1, R2 and R3 are three resistance connected in parallel to one another and R is the equivalent resistance of the circuit. A battery of V volts has been applied across the ends of this combination. When the switch of the key is closed, current I flows in the circuit such that 

10Ω and 10Ω are connected in series. Equivalent resistance of the circuit = 10Ω + 10Ω = 20Ω 

Q.21. Draw the paitern of magnetic field lines produced around a current-carrying straight conductor passing perpendicularly through horizontal cardboard. State and apply the right-hand thumb rule to mark the direction of the field lines. How will the strength of the magnetic field change when the point where magnetic field is to be determined is moved away from the straight conductor ? Give reason to justify your answer. 

Answer: Maxwell’s Right Hand Thumb rule states that if the current-carrying wire is imagined to be held in the right hand so that thumb points in the direction of current, then the direction in which fingers encircle the wire will give the direction of magnetic field lines around the wire. If we hold the current-carrying straight wire so that thumbs Magnetic field pattern due to a straight current-carrying wire in upward direction points the direction of current, the direction of magnetic field lines will be anticlockwise. The strength of the magnetic field is inversely proportional to the distance of the point of observation from the wire So, as we move away from the wire the strength of magnetic decreases Current (upwards).

Section – E 

Q.22. A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct? Write its correct value stating the reason. 

OR

Q.22. What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers? 

Answer: The value of pH for water is not correct. The correct value of pH of water is 7 because it has almost equal concentration of Hand OH, due to which it is neutral. 

OR 

Answer: Aluminium displaces the iron from iron sulphate and the colour of two solution changes from green to brown. No change takes place when copper strip is dipped in iron sulphate solution. No cfiange will be observed when iron strips are dipped in iron sulphate solution. The colour of the solution changes from green to colourless when zinc is added to iron sulphate solution. 

Q.23. What is observed when a pinch of sodium hydrogen carbonate is added to 2 mL of acetic acid taken in a test tube? Write chemical equation for the reaction involved in this case. 

Answer: CO2 gas is evolved with brisk effervescence when sodium hydrogen carbonate is added to acetic acid. 

Q.24. List in proper sequence four steps of obtaining germinating dicot seeds. OR After examining a prepared slide under the high power of a compound microscope, a student concludes that the given slide shows the various stages of binary fission in a unicellular organism. Write two observations on the basis of which such a conclusion may be drawn. 

Answer: 1. The root is formed when radicle of seed grows. 

2. The root grows downward into the soil and absorbs water and minerals from the soil. 

3. The shoot is formed from the upward growth of plumule. 

4. The green leaves are developed when the shoot comes above the ground. 

OR

Answer: 1. A single parent divides to form two daughter cells. 

2. The nucleus of mature cell seems elongated and a grove is formed in cell which divides the nucleus. 

Q.25. List four precautions which a student should observe while preparing a temporary mount of a leaf peel to show stomata in his school laboratory.

Answer: 1. Freshly plucked leaf should be taken for an epidermal peel. 

2. Hold the slide by its edges. 

3. Peel should be cut to a proper size. 

4. The peel should be allowed to dry. 

Q.26. Draw the path of a ray of light when it enters one of the faces of a glass slab at an angle of nearly 45°. Label 

(i) angle of refraction 

(ii) angle of emergence and 

(ii) lateral displacement. 

OR 

Q.26. A student traces the path of a ray of light through a glass prism as shown in the diagram, but leaves it incomplete and unlabelled. Redraw and complete the diagram. Also label on it zi, ze, zr, and ZD.

Answer: 

Q.27. The current flowing through a resistor connected in a circuit and the potential difference developed across its ends are as shown in the diagram by milliammeter and voltmeter readings respectively: 

(a) What are the least counts of these meters? 

(b) What is the resistance of the resistor? 

Answer: (a) 10 mA and 0.1 V 

(b) V = 2.4 volt, 1 = 250 mA = 0.25 A

From Ohm’s law. 

R=v/I = 2.4/0.25 = 9.6Ω

Science

Section – A

Q 1. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plant bearing white flowers. What will be the result in F₁progeny? 

Q 2. Write the energy conversion that takes place in a hydropower plant.

Q 3. A compound ‘X’ on heating with excess cone, sulphuric acid at 443 K gives an unsaturated compound ‘Y’. ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’. Identify ‘X’, ‘Y’ and Z’. Write the equation of the chemical reaction of the formation of ‘Y’ and also write the role of sulphuric acid in the reaction.

Q 4. (a) Name one gustatory receptor and one olfactory receptor present in human beings.

              (b) Write a and b in the given flow chart of the neuron through which information travels as an electrical impulse.

Dendrite → a → b → End Point of Neuron

Q 5. If the image formed by a spherical 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 labeled ray diagram to support your answer.

Q 6. Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light, and electrictiy.

Q 7. 2 ml of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with a dilute solution of a strong acid?

 OR

Q 7. The pH of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses. 

Q 8.(a) Why are most carbon compounds poor conductors of electricity?

             (b) Write the name and structure of a saturated compound in which the carbon atoms have arranged a ring.                        Give the number of single bonds present in this compound.

Q 9. Name the hormones secreted by the following endocrine glands and specify one function of each:

1. Thyroid
2. Pituitary
3. Pancreas

Q 10. Write one main difference between the asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival the one reproducing asexually or the one reproducing sexually ?

Give reasons to justify your answer.

Q 11. State the laws of refraction of light. Explain the term absolute refractive index of a medium’ and write an expression to relate it with the speed of light in vacuum.

OR

What is meant by power of a lens ? Write its SI unit. 

A student uses a lens of focal length 40 cm and another of -20 cm. Write the nature and power of each lens. 

Q 12.Show how would you join three resistors, each of resistance 9 Ω so that the equivalent resistance of the combination is (a) 13.5 Ω (b) 6 Ω?

OR

(a) Write Joule’s law of heating.

(b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V.

Q 13.(a) List the factors on which the resistance of a conductor in the shape of wire depends.

(b) Why are metals good conductors of electricity whereas glass is a bad conductor of electricity ? Give reason.

(c) Why are alloys commonly used in electrical heating devices ? Give reason.

Q 14.Students in a school listened to news read in the morning assembly that the mountains of garbage in Delhi, suddenly exploded and various vehicles got buried under it. Several people were also injured and there was a traffic jam all around. In the brain storming session the teacher also discussed this issue and asked the students to find out a solution to the problem of garbage. Finally they arrived at two main points—one is self management of the garbage we produce and the second is to generate less garbage at individual level.

(a) Suggest two measures to manage the garbage we produce.

(b) As an individual what can we do to generate the least garbage ? Give two points.

(c) List two values the teacher instilled in his students in this episode. 

Q 15.What is the dam ? Why do we seek to build large dams? While building large dams, which three main problems should particularly be addressed to maintain peace among local people? Mention them.

Q 16.(a) Write the steps involved in the extraction of pure metals in the middle of the activity series from carbonate ores.

(b) How is copper extracted from its sulfide ore? Explain the various steps supported by chemical equations. Draw labelled diagram for electrolytic refining of copper. 

Q 17. (a) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all three attempts.

(b) Name the scientist who first of all showed that the atomic number of an element is a more fundamental property than its atomic mass.

(c) State Modern Periodic law. 

Q 18.(a) Mention any two components of blood.

(b) Trace the movement of oxygenated blood in the body.

(c) Write the function of valves present in between atria and ventricles.

(d) Write one structural difference between the composition of artery and veins.

OR

(a) Define excretion.

(b) Name the basic filtration unit present in the kidney.

(c) Draw excretory system in human beings and label the following organs of excretory system which perform the following functions:

(i) forms urine.

(ii) is a long tube which collects urine from kidney.

(iii) Store urine until it is passed out.

Q 19.(a) Write the function of following parts in human female reproductive system:

(i) Ovary

(ii) Oviduct

(iii) Uterus

(b) Describe in brief the structure and function of placenta.

Q 20.(a) A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.

(b) Why do stars twinkle? Explain.

OR

(a) Write the function of each of the following parts of the human eye :

 (i) Cornea

(ii) Iris

(iii) Crystalline lens

(iv) Ciliary muscles

(b) Why does the sun appear reddish early in the morning? Will this phenomenon be observed by an astronaut on the Moon? Give a reason to justify your answer. 

Q 21.(a) State Fleming’s left-hand rule.

(b) Write the principle of working of an electric motor.

(c) Explain the function of the following parts of an electric motor:

 (i) Armature

(ii) Brushes

(iii) Split ring.

Section – B

Q 22.A student added few pieces of aluminium metal to two test tubes A and B containing aqueous solution of iron sulphate and copper sulphate. In the second part of her experiment, she added iron metal to another test tube C and D containing aqueous solution of aluminium sulphate and copper sulphate. 

In which test tube or test tubes will she observe colour change? 

On the basis of this experiment state which one is the most reactive metal and why?

Q 23. What is observed when a solution of sodium sulphate is added to a solution of barium chloride in a test tube? Write an equation for the chemical reaction involved and name the type of reaction in this case.

Q 24.List the steps of preparation of temporary mount of a leaf Peel to observe stomata.

Q 25. Name the process by which an amoeba reproduces. Draw the various stages of its reproduction in a proper sequence.

OR

Q 25. A student is viewing under a microscope a permanent slide showing various stages of asexual reproduction by budding in yeast. Draw a diagram of what he observes in the proper sequence.

Q 26. An object of height 4.0 cm is placed at a distance of 30 cm from optical centre ‘O’ of a convex lens of focal length 20 cm. Draw a ray diagram to find the position and size of the image formed. Mark optical centre ‘O’ and principal focus ‘F’ on the diagram. Also find the approximate ratio of size of image to the size of an object.

Q 27.The values of current (I) flowing through a given resistor of resistance (R), for the corresponding values of the potential difference (V) across the resistor are given below:

Plot a graph between current (I) and potential difference (V) and determine the resistance (R) of the resistor.

Answer

Answer 1: All the progeny of F₁ generation will have violet flowers because the violet colour is dominant over the recessive white colour.

Answer 2: In a hydropower plant, the potential energy of the water stored in a dam is converted into kinetic energy then the turbine converts the kinetic energy of falling water into mechanical energy and after that generator converts mechanical energy into electrical energy.

Answer 3:

X = CH₃CH₂OH-ethanol

Y = CH₂ = CH₂-ethene

CH₃CH₂OH + Na → CH₃CH₂ONa + H₂

Z = Hydrogen gas.

Here concentrated sulphuric acid acts as a dehydrating agent, it removes water molecules from ethanol.

Answer 4: (a) Tongue is the gustatory receptor present in the human body.

 (b) Dendrite → Cell body → Axon → End point of Neuron

Answer 5: Convex mirror always forms erect and diminished image.

 In the above ray diagram, the image formed is behind the mirror between pole (P) and focus (F), virtual, erect and diminished.

 Answer 6: Decomposition of zinc carbonate when the heat is applied.

Decomposition of water in presence of electricity:

Decomposition of silver chloride in the presence of light:

Answer 7: 

When a burning candle is brought towards the hydrogen gas, it burns with the pop sound and the candle will go off.

 When Zinc metal reacts with a dilute solution of strong acid then zinc chloride and hydrogen gas will be formed.

 OR

Answer 7.The salt commonly used to make tasty and crispy pakoras is baking soda i.e., sodium hydrogen carbonate (NaHCO₃).

 Chemical equation for its formation:

 Uses of Baking Soda:

1. It is used in the fire extinguisher.
2. It is also used as an ingredient of antacid.

Answer 8:

 (a) Electricity is conducted by moving electrons. But carbon forms covalent bonds by sharing of electrons. It does not have free electrons.

(b) Cyclohexane is a saturated compound in which carbon atoms are arranged in a ring.

There are 6 single bonds present in this compound.

Answer 9:

1. The thyroid gland secretes thyroxine. It regulates the metabolism and blood pressure of human beings.
2. The pituitary secretes growth hormone. It helps the bones and other body organs to grow properly.
3. The pancreas secretes insulin. Insulin helps to lower blood sugar level.

Answer 10: Asexual reproduction involves only one parent and the offsprings produced are clones and similar copies of their parents whereas sexual reproduction involves two parents and the offsprings produced are different from their parents. Offsprings produced by sexual reproduction have better chances of survival.

Sexual reproduction leads to variation because it leads to the formation of offspring by the combination of DNA from both parents, so the species will have better adaptability and better survival rate.

Answer 11:The two laws of refraction are:

 1. The Incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.

 2. The ratio of the sine of angle of incidence

     (i) to the sine of angle of refraction (r) at a point in a medium is constant, i.e., sin i /sin r = Constant

 Absolute refractive index: It is the ratio of the speed of light in vacuum (or air) to the speed of light in the given medium.

 OR

 The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it. It is also defined as the reciprocal of its focal length in metres.

The S.I. unit of power is dioptres (D).

Focal length of a convex lens is positive.

 So, lens having a focal length of 40 cm is convex.

 Focal length of a concave lens is negative.

 So, lens having focal length -20 cm is concave.

Answer 12:(a) To get an equivalent resistance of 13.5 Ω, the resistances should be connected as shown in the figure given below:

(b) To get an equivalent resistance of 6 Ω, the resistances should be connected as shown in the figure:

(a) According to Joule’s law of heating, the heat produced in a wire is directly proportional to

1. square of current (I₂),

2. resistance of wire (R),

3. time (t) for which current is passed.

Thus, the heat produced in the wire by current I in time ‘t’ is

 H ∝ I₂ Rt

H = K I₂ Rt

but K = 1, H = I₂ Rt

(b) We know that, P = VI

Answer 13:

 (a) Resistance of a conductor depends directly on its length, inversely proportional to the area of cross section, directly proportional to the temperature and it depends on the nature of the conductor.

(b) Metals have free electrons which can move and conduct electricity, whereas glass does not have free electrons which can flow freely to conduct electricity.

 (c) The resistivity of an alloy is generally higher than that of pure metal. Alloys do not oxidize (bum) readily at higher temperatures. Therefore, conductors of electric heating devices, such as toasters and electric irons, are made of an alloy rather than pure metal.

Answer 14:

(a) 1. Segregate the garbage produced into biodegradable and non- biodegradable waste.

      2. Stop using plastic bags instead of it more of cotton and jute bags should be used.

(b) 1. We should generate less garbage as much as possible.

      2. Recycling and reuse of materials should be adopted in order to minimise the waste.

 Answer 15: 

A dam is a barrier constructed to hold back water and raise its level forming a reservoir used to generate electricity or as a water supply.

Large dams are built in order to generate electricity from water supply.

While making large dams, social problems should be addressed. Proper rehabilitation should be provided to people.

Judicious use of people’s money should be done to ensure economic prosperity. Environmental problems, excessive cutting of trees, biological diversity loss should be checked.

Answer 16:(a) First the carbonate ore of a metal is heated in absence of air. This process is called calcination.

(b) Copper is extracted from sulphide ore ,by the process of roasting. It is done in the presence of air:

Answer 17: 

(a) 1. Dobereiner:

 Advantage: Group three elements having similar properties they were called as the Dobereiner triads. He arranged them in order of increasing atomic mass and the mass of the middle element was equal to the average of the other two elements.

Limitation: He was able to identify only 4 triads but he failed in his attempt to group nitrogen, phosphorus and arsenic because atomic mass of phosphorus is not the average of the other two.

      2. Newland:

Advantages: He arranged the elements in horizontal rows in order of increasing atomic mass. The property of every 8th element was similar to the 1st element.

Limitation: His arrangement was only applicable to lighter elements.

      3. Mendeleev:

Advantage: He arranged the elements in order of their increasing atomic mass and he corrected the mass of beryllium from 4.5 to 13.5 u.

Limitation: Position of hydrogen and isotopes were not justified in his periodic table.

(b) Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass.

(c) Modem periodic law states that “the properties of elements are a periodic function of their atomic number. Repetition of properties is due to the same outer electronic configuration.”

Answer 18:

(a) Red blood cells and white blood cells are the components of blood.

(b) The oxygenated blood goes into the left atrium from there it goes to the left ventricle and then to all the body organs.

(c) Valves prevents the backflow of blood from the ventricle to the atria.

(d) Walls of arteries are thick and they carry oxygenated blood whereas walls of veins are thin and they carry deoxygenated blood.

OR

(a) The process of removing toxic waste from the human body is called excretion.

(b) Nephron is the basic filtration unit present in the kidney.

Answer 19:

(a) (i) Ovary: It produces egg for fertilisation. It secretes estrogen and progesterone. Estrogen regulates secondary sexual characters and progesterone controls the thickness of the lining of the uterus.

(ii) Oviduct: It is the site of fertilization and carries eggs or fertilized ovum (zygote) to the uterus.

(iii) Uterus: It helps to nourish the fertilised ovum that will develop into a foetus. It holds the baby until it is ready for birth.

(b) Placenta is a disc shaped structure on uterine wall before implantation of an embryo. It provides oxygen and nutrients to the foetus.

It helps to remove waste also. The placenta is composed of both material tissues and tissue derived from the embryo. The chorion is the embryonic derived portion of the placenta. It is composed of fetal blood vessels and trophoblasts which are organized into finger-like structures called chorionic villi.

Answer 20:

(a) The boy is suffering from myopia.

This defect is caused:

1. due to increase in length of eyeball, and

2. decrease in focal length of eye lens, when the eye is fully relaxed.

Correction: The image of a distant object (i.e., at infinity) is formed in front of the retina of eye suffering from myopia as shown in fig.(a)

 As the image of the object lying at infinity is not formed on the retina of the eye, so such object can not be seen clearly by the myopic eye. The far point of such an eye is near to the eye as shown in fig. (b).

This defect can be corrected by using a concave lens (minus powered) of suitable focal length. So, a man suffering from this defect wears spectacles having a concave lens of suitable focal length. The concave lens diverges the rays of light entering the eye from infinity. Hence, this lens makes the rays of light appear to have come from the far point (O’) of the defective eye as shown in figure (c).

 (b) The twinkling of a star is due to atmospheric refraction of starlight. 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. This apparent position of the star is not stationary but keeps on changing slightly, as the physical conditions of the earth’s atmosphere are not stationary. Since the stars are very distant, they approximate point-sized sources of light. As the path of light rays coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers i.e., the star sometimes appear brighter, and at some other time, fainter, which is the twinkling effect.

OR

(a) (i) Cornea: It is a thin membrane, covering the surface of eyeball, through which light enters. It acts as a primary lens, which provides the refraction for light rays entering the eye.

(ii) Iris: It is a dark muscular dia-phragm that controls the size of the pupil and is located just behind the cornea in the eye.

(iii) Crystalline lens: It is converging in nature, made by the jelly like proteinaceous material. The focal length of the crystalline lens is changed by the ciliary muscles. Its function is to focus the incoming light rays from the object on the retina using its refractive property.

(iv) Ciliary muscles: It modifies the curvature and thereby the focal length of the eye lens by contract-ing or relaxing itself to focus the image of an object on the retina according to the distance of the object. It also holds the eye lens in position.

(b) At the sunrise, the light from the sun has to travel the longest distance to reach the observer. Therefore, the sun looks almost reddish because only red colour (λb < λr) which is least scattered, is received by our eye and appears to come from the sun. Hence, the appearance of the sun at sunrise, near the horizon looks almost reddish.

This phenomenon will not be observed by an astronaut on the Moon, since there is no atmosphere so no scattering of light takes place, thus the Sun appears dark.

Answer 21: (a) According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of the magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

(b) Principle of the electric motor: When a coil carrying current is placed in a magnetic field, it will experience a force. As a result of this force, the coil begins to rotate.

(c) (i) Armature: It creates a magnetic field and the second role is to generate an electromotive force.

(ii) Brushes: Carbon brushes are used to make contact with the rotating rings of the commutator and through them to supply current to the coil.

(iii) Split ring: Split rings are used to reverse the direction of current flowing through the coil every time the coil just passes the vertical position during a revolution.

Section – B

Answer 22: Only in test tubes A, B and D she will observe colour change from green to colourless in A because aluminium is more reactive than iron, it will displace iron. She will observe colour change from blue to colourless in test tube B. She will also observe colour change in test tube D from blue to light green. Aluminium is the most reactive metal because it displaces all the other three metals.

Answer 23:

It is an example of a double displacement reaction.

Answer 24:

1. Remove a peel from lower surface of leaf using forceps and put it in water.
2. Put a few drops of safranin stain in a watch glass.
3. After 2-3 mins, take out the peel and put it on a slide.
4. Put a drop of glycerine and put a coverslip over the peel.

Answer 25:

Amoeba reproduces by binary fission. It results in a division of nucleus followed by division of the cytoplasm.

Answer 26: Given, f = +20 cm, u = -30 cm, h0 = 4 cm

We know that,

Thus, the height or size of the image is 8 cm. The minus sign shows that this height is in the downward direction, that is, the image is formed below the axis.

Ratio of size of image to object = -8 /4 = -2

Object between F₁ and 2F₁

Image is formed beyond 2F₂, real, inverted.

Answer 27:

We know that, V = IR 

From the graph,

V = 0.5

I = 0.1

0.5 = 0.1 × R

⇒ R = 5 Ω