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CBSE Class 10 Science 2024 — Paper 31/4/3

80 marks · 3 hours · 39 questions (45 with the OR choices)

34 of its 45 questions also appear in 31/4/1 or 31/4/2; 11 are only in this paper.

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Questions 1–20 · 1 mark each

  1. Q1 1 mark

    Also in 31/4/1 (Q14), 31/4/2 (Q16)

    An electric iron of resistance draws a current of A. The heat developed in the iron in seconds is :
    1. (a)15000 J
    2. (b)6000 J
    3. (c)1500 J
    4. (d)3000 J
    Show answer
    (a) 15000 J
    Step-by-step solution →
  2. Q2 1 mark
    The acid produced in our stomach during digestion and the base used to neutralise the excess acid during indigestion respectively are :
    1. (a),
    2. (b),
    3. (c)Amino acids,
    4. (d)Lactic acid,
    Show answer
    (a) ,
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/4/1 (Q10), 31/4/2 (Q2)

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  4. Q4 1 mark

    Also in 31/4/1 (Q9), 31/4/2 (Q3)

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  5. Q5 1 mark

    Also in 31/4/1 (Q1)

    The above reaction is a :
    1. (a)Decomposition reaction
    2. (b)Displacement reaction
    3. (c)Double displacement reaction
    4. (d)Combination reaction
    Show answer
    (b) Displacement reaction
    Step-by-step solution →
  6. Q6 1 mark

    Also in 31/4/1 (Q3), 31/4/2 (Q7)

    Four solutions, namely glucose, alcohol, hydrochloric acid and sulphuric acid filled in four separate beakers are connected one by one in an electric circuit with a bulb. The solutions in which the bulb will glow when current is passed are :
    1. (a)Glucose and alcohol
    2. (b)Alcohol and hydrochloric acid
    3. (c)Glucose and sulphuric acid
    4. (d)Hydrochloric acid and sulphuric acid
    Show answer
    (d) Hydrochloric acid and sulphuric acid
    Step-by-step solution →
  7. Q7 1 mark

    Also in 31/4/1 (Q4), 31/4/2 (Q8)

    The metals which are found in both free state as well as combined state are :
    1. (a)Gold and platinum
    2. (b)Platinum and silver
    3. (c)Copper and silver
    4. (d)Gold and silver
    Show answer
    (c) Copper and silver
    Step-by-step solution →
  8. Q8 1 mark

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  9. Q9 1 mark

    Also in 31/4/1 (Q6), 31/4/2 (Q10)

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  10. Q10 1 mark

    Also in 31/4/1 (Q5), 31/4/2 (Q9)

    The number of single and double bonds present in a molecule of benzene () respectively, are :
    1. (a)6 and 6
    2. (b)9 and 3
    3. (c)3 and 9
    4. (d)3 and 3
    Show answer
    (b) 9 and 3
    Step-by-step solution →
  11. Q11 1 mark

    Also in 31/4/1 (Q7), 31/4/2 (Q5)

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  12. Q12 1 mark

    Also in 31/4/1 (Q16), 31/4/2 (Q11)

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  13. Q13 1 mark

    Also in 31/4/1 (Q15), 31/4/2 (Q12)

    A rectangular loop ABCD carrying a current is situated near a straight conductor XY, such that the conductor is parallel to the side AB of the loop and is in the plane of the loop. If a steady current is established in the conductor as shown, the conductor XY will
    X Y I B C A D I
    1. (a)remain stationary.
    2. (b)move towards the side AB of the loop.
    3. (c)move away from the side AB of the loop.
    4. (d)rotate about its axis.
    Show answer
    (b) move towards the side AB of the loop.
    Step-by-step solution →
  14. Q14 1 mark

    Also in 31/4/1 (Q11), 31/4/2 (Q13)

    Absolute refractive index of glass and water is and respectively. If the speed of light in glass is m/s, the speed of light in water is :
    1. (a) m/s
    2. (b) m/s
    3. (c) m/s
    4. (d) m/s
    Show answer
    (a) m/s
    Step-by-step solution →
  15. Q15 1 mark

    Also in 31/4/1 (Q12), 31/4/2 (Q14)

    When a beam of white light passes through a region having very fine dust particles, the colour of light mainly scattered in that region is :
    1. (a)Red
    2. (b)Orange
    3. (c)Blue
    4. (d)Yellow
    Show answer
    (c) Blue
    Step-by-step solution →
  16. Q16 1 mark

    Also in 31/4/1 (Q13), 31/4/2 (Q15)

    Consider the following combinations of resistors : The combinations having equivalent resistance is/are :
    2 Ω 2 Ω I 3 Ω 3 Ω 3 Ω II 2 Ω 4 Ω 3 Ω 3 Ω III 0.5 Ω 0.5 Ω IV
    1. (a)I and IV
    2. (b)Only IV
    3. (c)I and II
    4. (d)I, II and III
    Show answer
    (c) I and II
    Step-by-step solution →
  17. Q17 1 mark

    Also in 31/4/1 (Q20), 31/4/2 (Q17)

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  18. Q18 1 mark

    Also in 31/4/1 (Q19), 31/4/2 (Q20)

    For Questions number 17 to 20, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Magnetic field lines never intersect each other.

    Reason (R): If they intersect, then at the point of intersection, the compass needle would point towards two directions, which is not possible.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    Step-by-step solution →
  19. Q19 1 mark

    Also in 31/4/1 (Q17), 31/4/2 (Q19)

    For Questions number 17 to 20, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): The extraction of metals from their sulphide ores cannot take place without roasting of the ore.

    Reason (R): Roasting converts sulphide ores directly into metals.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (c) Assertion (A) is true, but Reason (R) is false.
    Step-by-step solution →
  20. Q20 1 mark

    Also in 31/4/1 (Q18)

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Questions 21–26 · 2 marks each

  1. Q21(a) 2 marks

    Also in 31/4/1 (Q23(a)), 31/4/2 (Q21(a))

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    OR
    Q21(b) 2 marks

    Also in 31/4/1 (Q23(b)), 31/4/2 (Q21(b))

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  2. Q22 2 marks
    When a soap is dissolved in water, the soap molecules form structures. What are these structures called ? Draw a labelled diagram of these structures.
    Show answer

    The structures are micelles: soap molecules cluster with hydrocarbon tails inwards and ionic ends facing the water.

    The structures are called micelles. In a micelle, soap molecules form a spherical cluster with their hydrocarbon (hydrophobic) tails pointing inwards, towards the centre where oily dirt collects, and their ionic (hydrophilic) ends on the outside facing the water, as shown in the labelled diagram.
    Step-by-step solution →
  3. Q23(a) 2 marks

    Also in 31/4/1 (Q21(a)), 31/4/2 (Q23(a))

    1 gram of solid sodium chloride was taken in a clean and dry test tube and concentrated sulphuric acid was added to it.
    1. (i)Name the gas evolved in the reaction.
    2. (ii)What will be observed when this gas is tested with (I) dry, and (II) wet blue litmus paper ? Write your conclusion about the nature (acidic/basic) of this gas.
    Show answer

    Hydrogen chloride gas; dry blue litmus is unchanged, wet blue litmus turns red, so the gas is acidic only with water.

    (i) Hydrogen chloride () gas is evolved. (ii) (I) Dry blue litmus paper shows no change — it stays blue; (II) Wet blue litmus paper turns red. Conclusion: hydrogen chloride gas is acidic in nature, but it shows its acidic character only in the presence of water, which lets it form () ions.
    Step-by-step solution →
    OR
    Q23(b) 2 marks

    Also in 31/4/1 (Q21(b)), 31/4/2 (Q23(b))

    Some metals react with acids to produce salt and hydrogen gas. Illustrate it with an example. How will you test the presence of this gas ?
    Show answer

    Zinc and dilute sulphuric acid give zinc sulphate and hydrogen; hydrogen burns with a pop sound near a flame.

    Example: zinc granules react with dilute sulphuric acid to form zinc sulphate (the salt) and hydrogen gas: . Test: pass the gas through soap solution and bring a burning candle near a gas-filled bubble (or bring a burning matchstick near the gas). The gas burns with a pop sound, which shows that it is hydrogen.
    Step-by-step solution →
  4. Q24 2 marks

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  5. Q25 2 marks
    What would have been the colour of the sky, if the Earth had no atmosphere ? Give reason to justify your answer.
    Show answer

    The sky would appear dark (black), because with no atmosphere nothing would scatter sunlight towards us.

    The sky would appear dark (black). The sky looks blue only because the molecules of air and other fine particles in the atmosphere scatter sunlight, blue light most strongly, towards our eyes from all directions. With no atmosphere there would be nothing to scatter the sunlight, so no light would reach us from the sky except directly from the Sun, and the sky would look dark.
    Step-by-step solution →
  6. Q26 2 marks
    Calculate the resistance of a copper wire of length m and area of cross-section . Resistivity of copper is .
    Show answer

    The resistance of the copper wire is .

    The resistance of the copper wire is .
    Step-by-step solution →

Questions 27–33 · 3 marks each

  1. Q27 3 marks

    Also in 31/4/1 (Q31), 31/4/2 (Q28)

    Define the term power of accommodation of human eye. What happens to the image distance in the eye when we increase the distance of an object from the eye ? Name and explain the role of the part of human eye responsible for it in this case.
    Show answer

    Power of accommodation is the eye lens's ability to change its focal length; image distance stays fixed as the ciliary muscles relax.

    Power of accommodation: the ability of the eye lens to adjust its focal length (by changing its curvature) so that we can see both nearby and distant objects clearly. When the object is moved farther from the eye, the image distance does not change — the image is still formed on the retina, whose distance from the eye lens is fixed; instead, the focal length of the eye lens changes. The part responsible is the ciliary muscles, which hold the eye lens and change its curvature. As the object moves away, the ciliary muscles relax, the eye lens becomes thinner and its focal length increases, so the image is still focused sharply on the retina.
    Step-by-step solution →
  2. Q28 3 marks
    Write chemical equations for the following reactions, giving the conditions for the reaction in each case :
    1. (a)Reaction of ethanol with ethanoic acid
    2. (b)Reaction of an ester with a base ()
    3. (c)Formation of ethene from ethanol
    Show answer

    Esterification needs warm conc. , saponification needs heating with NaOH, and ethanol gives ethene at 443 K with conc. .

    (a) . Condition: a few drops of concentrated sulphuric acid as catalyst, warming. (b) . Condition: heating with sodium hydroxide solution (saponification). (c) . Condition: heating at K with excess concentrated sulphuric acid, which acts as a dehydrating agent.
    Step-by-step solution →
  3. Q29 3 marks

    Also in 31/4/1 (Q32)

    A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the centre of it. He sprinkles some iron filings uniformly around the bar magnet. Then he taps the drawing board gently and observes that the iron filings arrange themselves in a particular pattern.
    1. (a)Why do iron filings arrange in a particular pattern ?
    2. (b)What does the crowding of iron filings at the ends of the magnet indicate ?
    3. (c)What do the lines, along which the iron filings align, represent ?
    4. (d)If the student places a cardboard horizontally in a current carrying solenoid and repeats the above activity, in what pattern would the iron filings arrange ? State the conclusion drawn about the magnetic field based on the observed pattern of the lines.
    Show answer

    Filings align along field lines; crowding at the poles shows the strongest field; inside a solenoid parallel lines show a uniform field.

    (a) The bar magnet exerts a force on the iron filings in the region around it — its magnetic field. Each filing becomes a tiny magnet and turns to lie along the direction of the field at its position; tapping lets the filings move freely, so together they arrange themselves in a definite pattern. (b) The crowding of the filings at the ends shows that the magnetic field is strongest near the poles of the magnet. (c) The lines along which the filings align represent magnetic field lines. (d) Inside the solenoid the iron filings arrange themselves in parallel straight lines (outside, the pattern is like that of a bar magnet). Conclusion: the magnetic field inside a current-carrying solenoid is the same at all points — it is uniform.
    Step-by-step solution →
  4. Q30 3 marks

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  5. Q31 3 marks

    Also in 31/4/1 (Q27)

    Write the common name and the chemical name of the compound . Write the method of its preparation. Give chemical equation for the reaction, when water reacts with .
    Show answer

    It is Plaster of Paris, calcium sulphate hemihydrate; gypsum heated at 373 K gives it, and with water it sets back into gypsum.

    Common name: Plaster of Paris. Chemical name: calcium sulphate hemihydrate. Preparation: gypsum () is heated at K; it loses water and forms Plaster of Paris: . Reaction with water: on mixing with water, Plaster of Paris changes back into gypsum, giving a hard solid mass: .
    Step-by-step solution →
  6. Q32(a) 3 marks

    Also in 31/4/1 (Q29(a)), 31/4/2 (Q33(a))

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    OR
    Q32(b) 3 marks

    Also in 31/4/1 (Q29(b)), 31/4/2 (Q33(b))

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  7. Q33 3 marks

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Questions 34–36 · 5 marks each

  1. Q34(a) 5 marks

    Also in 31/4/1 (Q35(a)), 31/4/2 (Q36(a))

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    OR
    Q34(b) 5 marks

    Also in 31/4/1 (Q35(b)), 31/4/2 (Q36(b))

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  2. Q35(a) 5 marks

    Also in 31/4/1 (Q34(a))

    What is a chemical reaction? Describe one activity each to show that a chemical change has occurred in which
    1. (i)change of colour, and
    2. (ii)change in temperature has taken place.
    Show answer

    A chemical reaction forms new substances; iron in copper sulphate shows a colour change, and quick lime in water shows a temperature rise.

    A chemical reaction is a process in which one or more substances (reactants) change into new substances (products) with a different composition and different properties. (i) Change of colour: hang a clean iron nail in blue copper sulphate solution for about 20 minutes. The solution turns light green and the nail gets a reddish-brown coating, because iron displaces copper: . (ii) Change in temperature: add water slowly to a small amount of quick lime (calcium oxide) in a beaker. The beaker becomes hot, because the reaction releases heat: .
    Step-by-step solution →
    OR
    Q35(b) 5 marks

    Also in 31/4/1 (Q34(b))

    1. (i)Define a decomposition reaction. How can we say that (I) electrolysis of water, and (II) blackening of silver bromide when exposed to sunlight, are decomposition reactions? Mention the type of energy involved in each case.
    2. (ii)“The type of reactions in which (I) calcium oxide is formed, and (II) calcium hydroxide is formed are opposite reactions to each other.” Justify this statement with the help of chemical equations.
    Show answer

    Decomposition breaks one reactant into simpler products (electrical and light energy here); calcium oxide forms by decomposition and calcium hydroxide by combination, opposite types.

    (i) A decomposition reaction is one in which a single reactant breaks down to give two or more simpler products. (I) In electrolysis of water, one reactant, water, breaks into hydrogen and oxygen: ; the energy involved is electrical energy. (II) In sunlight, silver bromide breaks into silver, which makes it grey-black, and bromine: ; the energy involved is light energy. So both are decomposition reactions. (ii) (I) Calcium oxide is formed by decomposition, one reactant giving two products: . (II) Calcium hydroxide is formed by combination, two reactants giving one product: . Decomposition splits one substance into simpler ones while combination joins substances into one, so the two types are opposite reactions.
    Step-by-step solution →
  3. Q36(a) 5 marks
    1. (i)State laws of reflection of light.
    2. (ii)An object of height cm is placed at cm in front of a concave mirror of focal length cm. At what distance from the mirror should a screen be placed, so that a focussed image is obtained on it ? Find the height of the image.
    Show answer

    Screen 30 cm in front of the mirror ( cm); the image is 10 cm tall, real and inverted.

    (i) (1) The angle of incidence is equal to the angle of reflection. (2) The incident ray, the normal to the mirror at the point of incidence and the reflected ray all lie in the same plane. (ii) The screen should be placed cm in front of the mirror ( cm). The height of the image is cm: the image is cm tall, real and inverted (magnification ).
    Step-by-step solution →
    OR
    Q36(b) 5 marks
    1. (i)State laws of refraction of light.
    2. (ii)Draw a ray diagram to show refraction of a ray of light through a rectangular glass slab. How is the emergent ray related to incident ray ? Mark lateral displacement in the diagram.
    Show answer

    The laws: coplanar rays and constant ; through a slab the emergent ray is parallel to the incident ray but laterally shifted.

    (i) (1) The incident ray, the refracted ray and the normal to the interface of the two media at the point of incidence all lie in the same plane. (2) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for light of a given colour and a given pair of media (, Snell's law). (ii) In the ray diagram the ray bends towards the normal on entering the glass slab and away from the normal on leaving it. The emergent ray is parallel to the incident ray () but shifted sideways; the lateral displacement is the perpendicular distance between the incident ray produced and the emergent ray, marked in the diagram.
    Step-by-step solution →

Questions 37–39 · 4 marks each

  1. Q37 4 marks

    Also in 31/4/1 (Q39), 31/4/2 (Q37)

    Study the following circuit: On the basis of this circuit, answer the following questions:
    A B C 4 Ω 6 Ω 16 Ω 8 Ω 8 Ω 6 V Key
    1. (a)Find the value of total resistance between the points A and B.[1]
    2. (b)Find the resistance between the points B and C.[1]
    3. (c)(i)Calculate the current drawn from the battery, when the key is closed.[2]
    4. (c)(ii)OR : In the above circuit, the resistor or the parallel combination of two resistors of , which one of the two will have more potential difference across its two ends? Justify your answer.[2]
    Show answer

    and ; A; or the resistor has the larger potential difference, 3.2 V against 0.8 V.

    (a) . (b) , so . (c)(i) Total resistance , so the current drawn from the battery is A. (c)(ii) The resistor. It is in series with the parallel combination, so the same current, 0.2 A, flows through both; by the potential difference is V across the resistor but only V across the combination, whose resistance is .
    Step-by-step solution →
  2. Q38 4 marks

    Also in 31/4/1 (Q37), 31/4/2 (Q38)

    Three metal samples of magnesium, aluminium and iron were taken and rubbed with sand paper. These samples were then put separately in test tubes containing dilute hydrochloric acid. Thermometers were also suspended in each test tube so that their bulbs dipped in the acid. The rate of formation of bubbles was observed. The above activity was repeated with dilute nitric acid and the observations were recorded. Answer the following questions:
    1. (a)When activity was done with dilute hydrochloric acid, then in which one of the test tubes was the rate of formation of bubbles the fastest and the thermometer showed the highest temperature?[1]
    2. (b)Which metal did not react with dilute hydrochloric acid? Give reason.[1]
    3. (c)(i)Why is hydrogen gas not evolved when a metal reacts with dilute nitric acid? Name the ultimate products formed in the reaction.[2]
    4. (c)(ii)OR : Name the type of reaction on the basis of which reactivity of metals is decided. You have two metals X and Y. How would you decide which is more reactive than the other?[2]
    Show answer

    Magnesium reacts fastest with hydrochloric acid; none of the three metals fails to react; nitric acid oxidises hydrogen to water; displacement reactions decide reactivity.

    (a) The test tube with magnesium. Magnesium is the most reactive of the three, so it displaces hydrogen from dilute hydrochloric acid fastest and releases the most heat: . (b) None of the three metals fails to react. Magnesium, aluminium and iron all lie above hydrogen in the activity series, so each displaces hydrogen from dilute hydrochloric acid; iron reacts the most slowly. Only a metal below hydrogen, such as copper, does not react with dilute hydrochloric acid, because it cannot displace hydrogen from the acid. (c)(i) Nitric acid is a strong oxidising agent: it oxidises the hydrogen produced to water and is itself reduced to an oxide of nitrogen (, or ). The ultimate products are the metal nitrate, water and an oxide of nitrogen. (c)(ii) Displacement reactions. Dip a strip of metal X in a solution of a salt of Y, and a strip of Y in a solution of a salt of X. If X displaces Y, so that Y is deposited on X, X is more reactive than Y; if instead Y displaces X, Y is more reactive. For example, iron displaces copper from copper sulphate solution, so iron is more reactive than copper.
    Step-by-step solution →
  3. Q39 4 marks

    Also in 31/4/1 (Q38), 31/4/2 (Q39)

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