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CBSE Class 10 Science 2024 — Paper 31/4/1

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

40 of its 45 questions also appear in 31/4/2 or 31/4/3; 5 are only in this paper.

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Questions 1–20 · 1 mark each

  1. Q1 1 mark

    Also in 31/4/3 (Q5)

    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 →
  2. Q2 1 mark

    Also in 31/4/2 (Q6)

    An aqueous solution of a salt turns blue litmus to red. The salt could be the one obtained by the reaction of :
    1. (a) and
    2. (b) and
    3. (c) and
    4. (d) and
    Show answer
    (d) and
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/4/2 (Q7), 31/4/3 (Q6)

    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 →
  4. Q4 1 mark

    Also in 31/4/2 (Q8), 31/4/3 (Q7)

    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 →
  5. Q5 1 mark

    Also in 31/4/2 (Q9), 31/4/3 (Q10)

    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 →
  6. Q6 1 mark

    Also in 31/4/2 (Q10), 31/4/3 (Q9)

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  7. Q7 1 mark

    Also in 31/4/2 (Q5), 31/4/3 (Q11)

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  8. Q8 1 mark

    Also in 31/4/2 (Q4)

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  9. Q9 1 mark

    Also in 31/4/2 (Q3), 31/4/3 (Q4)

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  10. Q10 1 mark

    Also in 31/4/2 (Q2), 31/4/3 (Q3)

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  11. Q11 1 mark

    Also in 31/4/2 (Q13), 31/4/3 (Q14)

    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 →
  12. Q12 1 mark

    Also in 31/4/2 (Q14), 31/4/3 (Q15)

    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 →
  13. Q13 1 mark

    Also in 31/4/2 (Q15), 31/4/3 (Q16)

    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 →
  14. Q14 1 mark

    Also in 31/4/2 (Q16), 31/4/3 (Q1)

    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 →
  15. Q15 1 mark

    Also in 31/4/2 (Q12), 31/4/3 (Q13)

    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 →
  16. Q16 1 mark

    Also in 31/4/2 (Q11), 31/4/3 (Q12)

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  17. Q17 1 mark

    Also in 31/4/2 (Q19), 31/4/3 (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 →
  18. Q18 1 mark

    Also in 31/4/3 (Q20)

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  19. Q19 1 mark

    Also in 31/4/2 (Q20), 31/4/3 (Q18)

    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 →
  20. Q20 1 mark

    Also in 31/4/2 (Q17), 31/4/3 (Q17)

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Questions 21–26 · 2 marks each

  1. Q21(a) 2 marks

    Also in 31/4/2 (Q23(a)), 31/4/3 (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
    Q21(b) 2 marks

    Also in 31/4/2 (Q23(b)), 31/4/3 (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 →
  2. Q22 2 marks
    Distinguish between a saturated and an unsaturated hydrocarbon by flame test. List the products of combustion reaction of a saturated hydrocarbon.
    Show answer

    Saturated hydrocarbons burn with a clean blue flame, unsaturated ones with a sooty yellow flame; combustion gives carbon dioxide and water.

    Flame test: a saturated hydrocarbon burns in air with a clean, blue flame without smoke, whereas an unsaturated hydrocarbon burns with a yellow flame giving lots of black smoke (soot). Products of combustion of a saturated hydrocarbon: carbon dioxide and water, with the release of heat and light — e.g. .
    Step-by-step solution →
  3. Q23(a) 2 marks

    Also in 31/4/2 (Q21(a)), 31/4/3 (Q21(a))

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    OR
    Q23(b) 2 marks

    Also in 31/4/2 (Q21(b)), 31/4/3 (Q21(b))

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  4. Q24 2 marks

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  5. Q25 2 marks
    A person suffering from presbyopia needs bifocal lens. If he needs two lens of power dioptre and dioptre, which one of these two lenses is for the correction of distant vision and what is its focal length ?
    Show answer

    The concave lens of power D corrects distant vision; its focal length is cm.

    The concave lens of power D (the upper part of the bifocal lens) is for the correction of distant vision. Its focal length is m cm; the minus sign shows that it is a diverging (concave) lens.
    Step-by-step solution →
  6. Q26 2 marks
    Two wires A and B of same material, having same lengths and diameters mm and mm respectively, are connected one by one in a circuit. Which one of these two wires will offer more resistance to the flow of current in the circuit ? Justify your answer.
    Show answer

    Wire A, the thinner wire, offers more resistance: is 2.25 times .

    Wire A (diameter mm) offers more resistance. For wires of the same material and length, with , so . Hence : the thinner wire A has the smaller area of cross-section and times the resistance of wire B.
    Step-by-step solution →

Questions 27–33 · 3 marks each

  1. Q27 3 marks

    Also in 31/4/3 (Q31)

    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 →
  2. Q28 3 marks

    Also in 31/4/2 (Q31)

    Why is the conversion of ethanol to ethanoic acid an oxidation reaction ? Name the oxidising agent used in this conversion. Write chemical equation for this oxidation reaction. How is this reaction different from the reaction in which ethanol burns in the presence of oxygen ?
    Show answer

    Ethanol gains oxygen and loses hydrogen, so it is oxidised to ethanoic acid by alkaline ; unlike burning, it is a controlled partial oxidation.

    It is an oxidation because oxygen is added to ethanol and hydrogen is removed from it: () gains one oxygen atom and loses two hydrogen atoms to become (). Oxidising agent: alkaline potassium permanganate (or acidified potassium dichromate). Equation: , i.e. . Difference: this is a controlled (partial) oxidation by an oxidising agent, without burning — the two-carbon chain is kept and ethanoic acid is formed. When ethanol burns in oxygen it undergoes complete oxidation (combustion) with a flame, forming only carbon dioxide and water with the release of heat and light: .
    Step-by-step solution →
  3. Q29(a) 3 marks

    Also in 31/4/2 (Q33(a)), 31/4/3 (Q32(a))

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    Q29(b) 3 marks

    Also in 31/4/2 (Q33(b)), 31/4/3 (Q32(b))

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  4. Q30 3 marks

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  5. Q31 3 marks

    Also in 31/4/2 (Q28), 31/4/3 (Q27)

    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 →
  6. Q32 3 marks

    Also in 31/4/3 (Q29)

    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 →
  7. Q33 3 marks

    Also in 31/4/2 (Q29)

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Questions 34–36 · 5 marks each

  1. Q34(a) 5 marks

    Also in 31/4/3 (Q35(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
    Q34(b) 5 marks

    Also in 31/4/3 (Q35(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 →
  2. Q35(a) 5 marks

    Also in 31/4/2 (Q36(a)), 31/4/3 (Q34(a))

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    Q35(b) 5 marks

    Also in 31/4/2 (Q36(b)), 31/4/3 (Q34(b))

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  3. Q36(a) 5 marks

    Also in 31/4/2 (Q35(a))

    The variation of image distance with object distance for a convex lens is given in the following observation table. Analyse it and answer the questions that follow:
    1. (i)Without calculation, find the focal length of the convex lens. Justify your answer.
    2. (ii)Which observation is not correct? Why? Draw ray diagram to find the position of the image formed for this position of the object.
    3. (iii)Find the approximate value of magnification for cm.
    S. No.Object distance (u) cmImage distance (v) cm
    1
    2
    3
    4
    5
    6
    Show answer

    cm; observation 6 is wrong as should be cm; the magnification for cm is .

    (i) cm. In observation 3 the object and the image are at the same distance, 50 cm, on opposite sides of the lens; this happens only when the object is at 2F₁ and the image at 2F₂, so cm and cm. (ii) Observation 6 ( cm, cm) is not correct. The object at 15 cm is between the optical centre and F₁ (), so the lens forms a virtual, erect, magnified image on the same side as the object and must be negative. By the lens formula the image is at cm and is 2.5 times the size of the object, as the ray diagram shows. (iii) : the image is real, inverted and 5 times the size of the object.
    Step-by-step solution →
    OR
    Q36(b) 5 marks

    Also in 31/4/2 (Q35(b))

    1. (i)Define principal axis of a lens. Draw a ray diagram to show what happens when a ray of light parallel to the principal axis of a concave lens passes through it.
    2. (ii)The focal length of a concave lens is 20 cm. At what distance from the lens should a 5 cm tall object be placed so that its image is formed at a distance of 15 cm from the lens? Also calculate the size of the image formed.
    Show answer

    The object must be 60 cm in front of the lens; the image is 1.25 cm tall, virtual and erect.

    (i) The principal axis of a lens is the imaginary straight line passing through the two centres of curvature of the lens. A ray parallel to the principal axis, after refraction through a concave lens, diverges (bends away from the axis) and appears to come from the principal focus F₁ on the same side of the lens as the incident light, as shown in the ray diagram. (ii) With cm and cm, , so cm: the object must be placed 60 cm in front of the lens. Then and cm: the image is 1.25 cm tall, virtual and erect.
    Step-by-step solution →

Questions 37–39 · 4 marks each

  1. Q37 4 marks

    Also in 31/4/2 (Q38), 31/4/3 (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 →
  2. Q38 4 marks

    Also in 31/4/2 (Q39), 31/4/3 (Q39)

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  3. Q39 4 marks

    Also in 31/4/2 (Q37), 31/4/3 (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 .
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