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CBSE Class 10 Science 2024 — Paper 31/5/2

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

34 of its 45 questions also appear in 31/5/1 or 31/5/3; 11 are only in this paper.

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Questions 1–20 · 1 mark each

  1. Q1 1 mark
    Which of the following is not a thermal decomposition reaction ?
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (c)
    Step-by-step solution →
  2. Q2 1 mark

    Also in 31/5/1 (Q6), 31/5/3 (Q9)

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  3. Q3 1 mark

    Also in 31/5/1 (Q8), 31/5/3 (Q10)

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  4. Q4 1 mark

    Also in 31/5/1 (Q9), 31/5/3 (Q2)

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  5. Q5 1 mark

    Also in 31/5/1 (Q2), 31/5/3 (Q6)

    Which of the following is a redox reaction, but not a combination reaction ?
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (d)
    Step-by-step solution →
  6. Q6 1 mark

    Also in 31/5/1 (Q3)

    The salt present in tooth enamel is :
    1. (a)Calcium phosphate
    2. (b)Magnesium phosphate
    3. (c)Sodium phosphate
    4. (d)Aluminium phosphate
    Show answer
    (a) Calcium phosphate
    Step-by-step solution →
  7. Q7 1 mark

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  8. Q8 1 mark

    Also in 31/5/1 (Q4), 31/5/3 (Q7)

    An aqueous solution of sodium chloride is prepared in distilled water. The pH of this solution is :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (c)
    Step-by-step solution →
  9. Q9 1 mark

    Also in 31/5/1 (Q5), 31/5/3 (Q8)

    A metal ‘X’ is used in thermit process. When ‘X’ is heated with oxygen, it gives an oxide ‘Y’, which is amphoteric in nature. ‘X’ and ‘Y’ respectively are :
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (b)
    Step-by-step solution →
  10. Q10 1 mark

    Also in 31/5/1 (Q16), 31/5/3 (Q11)

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  11. Q11 1 mark

    Also in 31/5/1 (Q15), 31/5/3 (Q12)

    A uniform magnetic field exists in the plane of paper as shown in the diagram. In this field, an electron () and a positron () enter as shown. The electron and positron experience forces :
    e⁻ p⁺ Uniform magnetic field
    1. (a)both pointing into the plane of the paper.
    2. (b)both pointing out of the plane of the paper.
    3. (c)pointing into the plane of the paper and out of the plane of the paper respectively.
    4. (d)pointing out of the plane of the paper and into the plane of the paper respectively.
    Show answer
    (a) both pointing into the plane of the paper.
    Step-by-step solution →
  12. Q12 1 mark

    Also in 31/5/1 (Q14), 31/5/3 (Q16)

    The current carrying device which produces a magnetic field similar to that of a bar magnet is :
    1. (a)A straight conductor
    2. (b)A circular loop
    3. (c)A solenoid
    4. (d)A circular coil
    Show answer
    (c) A solenoid
    Step-by-step solution →
  13. Q13 1 mark

    Also in 31/5/1 (Q10), 31/5/3 (Q1)

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  14. Q14 1 mark

    Also in 31/5/1 (Q11), 31/5/3 (Q13)

    How will the image formed by a convex lens be affected, if the upper half of the lens is wrapped with a black paper ?
    1. (a)The size of the image formed will be one-half of the size of the image due to complete lens.
    2. (b)The image of upper half of the object will not be formed.
    3. (c)The brightness of the image will reduce.
    4. (d)The lower half of the inverted image will not be formed.
    Show answer
    (c) The brightness of the image will reduce.
    Step-by-step solution →
  15. Q15 1 mark

    Also in 31/5/1 (Q12), 31/5/3 (Q14)

    The phenomena of light involved in the formation of rainbow are :
    1. (a)Refraction, reflection and dispersion
    2. (b)Refraction, dispersion and internal reflection
    3. (c)Reflection, dispersion and internal reflection
    4. (d)Refraction, dispersion, scattering and total internal reflection
    Show answer
    (b) Refraction, dispersion and internal reflection
    Step-by-step solution →
  16. Q16 1 mark

    Also in 31/5/1 (Q13), 31/5/3 (Q15)

    The colour of light for which the refractive index of glass is minimum, is :
    1. (a)Red
    2. (b)Yellow
    3. (c)Green
    4. (d)Violet
    Show answer
    (a) Red
    Step-by-step solution →
  17. Q17 1 mark

    Also in 31/5/1 (Q20)

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  18. Q18 1 mark

    Also in 31/5/1 (Q17), 31/5/3 (Q18)

    Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Some vegetable oils are healthy.

    Reason (R): Vegetable oils generally have long unsaturated carbon chains.

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

    Also in 31/5/1 (Q18), 31/5/3 (Q19)

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  20. Q20 1 mark

    Also in 31/5/1 (Q19), 31/5/3 (Q17)

    Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) and (d) as given below.

    Assertion (A): Electrons move from lower potential to higher potential in a conductor.

    Reason (R): A dry cell maintains electric potential difference across the ends of a conductor.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the 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
    (b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    Step-by-step solution →

Questions 21–26 · 2 marks each

  1. Q21(a) 2 marks

    Also in 31/5/1 (Q23(a)), 31/5/3 (Q21(a))

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    OR
    Q21(b) 2 marks

    Also in 31/5/1 (Q23(b)), 31/5/3 (Q21(b))

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  2. Q22 2 marks
    Identify the functional group present in the following compounds and also name them :
    (a) H C C OH H O H (b) H C H O
    Show answer

    (a) Carboxylic acid group in ethanoic acid; (b) aldehyde group in methanal.

    (a) The functional group is the carboxylic acid group, , and the compound is ethanoic acid (acetic acid), . (b) The functional group is the aldehyde group, , and the compound is methanal (formaldehyde), .
    Step-by-step solution →
  3. Q23(a) 2 marks

    Also in 31/5/1 (Q21(a)), 31/5/3 (Q23(a))

    Copper powder is taken in a china dish and heated over a burner. Name the product formed and state its colour. Write the chemical equation for the reaction involved.
    Show answer

    Heated copper powder forms black copper(II) oxide, : .

    The product is copper(II) oxide, , which is black: the reddish-brown surface of the copper powder becomes coated with it. Equation: .
    Step-by-step solution →
    OR
    Q23(b) 2 marks

    Also in 31/5/1 (Q21(b)), 31/5/3 (Q23(b))

    Write chemical equation for the chemical reaction which occurs when the aqueous solutions of barium chloride and sodium sulphate react together. Write the symbols of the ions present in the compound precipitated in the reaction.
    Show answer

    The precipitate is barium sulphate, , which contains and ions.

    . The precipitate is barium sulphate, , a white solid; the ions present in it are the barium ion, , and the sulphate ion, .
    Step-by-step solution →
  4. Q24 2 marks

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  5. Q25 2 marks
    Define power of a lens. Find power of a lens whose focal length is 50 cm.
    Show answer

    Power is the reciprocal of focal length in metres, , measured in dioptres; the lens has D.

    Power of a lens is the reciprocal of its focal length expressed in metres, ; it measures the degree of convergence or divergence of light that the lens produces, and its SI unit is the dioptre (D), the power of a lens of focal length 1 m. For cm m: D, a converging (convex) lens.
    Step-by-step solution →
  6. Q26 2 marks
    An electric source can supply a charge of 750 coulomb. If the current drawn by a device is 15 mA, find the time in which the electric source will be discharged completely.
    Show answer

    The electric source is discharged completely in s (about 13.9 hours).

    Using : s, that is s (about hours).
    Step-by-step solution →

Questions 27–33 · 3 marks each

  1. Q27(a) 3 marks

    Also in 31/5/1 (Q31(a)), 31/5/3 (Q33(a))

    Study the diagram given below and answer the questions that follow :
    1. (i)Name the defect of vision depicted in this diagram stating the part of the eye responsible for this condition.
    2. (ii)List two causes of this defect.
    3. (iii)Name the type of lens used to correct this defect and state its role in this case.
    N N′
    Show answer

    Hypermetropia arises when the eye lens has too long a focal length (or the eyeball is too small); a convex lens adds converging power.

    (i) The defect is hypermetropia (far-sightedness): light from the nearby point N′ is brought to a focus behind the retina. The part of the eye responsible is the eye lens, whose focal length has become too long (an eyeball that has become too small has the same effect). (ii) Two causes: (1) the focal length of the eye lens is too long; (2) the eyeball has become too small. (iii) A convex (converging) lens of suitable power. It provides the additional converging power needed: it bends the rays from a nearby object so that they appear to come from a farther point that the eye can focus, so the image is formed on the retina.
    Step-by-step solution →
    OR
    Q27(b) 3 marks

    Also in 31/5/1 (Q31(b)), 31/5/3 (Q33(b))

    What is dispersion of white light ? State its cause. Draw a diagram to show dispersion of a beam of white light by a glass prism.
    Show answer

    Dispersion is the splitting of white light into VIBGYOR, because the refractive index of glass differs for each colour.

    Dispersion is the splitting of white light into its component colours, violet, indigo, blue, green, yellow, orange and red (VIBGYOR), when it passes through a glass prism; the band of colours obtained is called a spectrum. Cause: the different colours of light bend through different angles with respect to the incident ray as they pass through the prism, because the refractive index of glass (and so the speed of light in glass) is different for different colours; red bends the least and violet the most, so the colours emerge along different paths and separate. Diagram: a beam of white light entering one face of the prism bends towards the normal and starts to split; at the second face the colours bend away from the normal and fall on a screen as a spectrum, with red least deviated and violet, nearest the base, most deviated.
    Step-by-step solution →
  2. Q28 3 marks
    Suggest an activity to differentiate between the chemical properties (acidic or basic character) of the product obtained on burning a metal (magnesium) and a non-metal (sulphur).
    Show answer

    The solution of burnt magnesium turns red litmus blue (basic), while that of burnt sulphur turns blue litmus red (acidic).

    Activity: Burn a cleaned magnesium ribbon held in tongs; it burns with a dazzling white flame and leaves white ash, magnesium oxide. Dissolve the ash in a little water and test it with litmus: red litmus turns blue, so the solution is basic. Burn sulphur powder in a deflagrating spoon and collect the gas, sulphur dioxide, in a test tube held upside down over it; add a little water, shake and test with litmus: blue litmus turns red, so the solution is acidic. Equations: , ; , . Conclusion: the oxide of the metal (magnesium) is basic and the oxide of the non-metal (sulphur) is acidic.
    Step-by-step solution →
  3. Q29 3 marks

    Also in 31/5/1 (Q27)

    Study the experimental set-up shown in the diagram and write chemical equation for the chemical reaction involved. Name and define the type of reaction. List two other metals which can be used in place of iron to show the same type of reaction with copper sulphate solution.
    Stand Test tube Thread Copper sulphate solution Iron nail
    Show answer

    Iron displaces copper from copper sulphate, a displacement reaction; zinc and magnesium (or aluminium), being above copper, can replace iron.

    Equation: ; the iron nails become coated with brownish copper and the blue colour of the solution fades. Type: displacement reaction, a reaction in which a more reactive element displaces a less reactive element from its compound (here iron, being more reactive, displaces copper from copper sulphate). Two other metals that can be used in place of iron: zinc and magnesium, both above copper in the reactivity series (; ). Aluminium also lies above copper and displaces it, so any two of magnesium, aluminium and zinc are correct. Lead lies above copper as well, but the lead sulphate it forms is insoluble and coats the lead, so in copper sulphate solution the reaction soon stops and the copper coating and the fading blue colour do not develop.
    Step-by-step solution →
  4. Q30 3 marks

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  5. Q31 3 marks

    Also in 31/5/1 (Q29)

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  6. Q32 3 marks
    “Earth wire is a safety measure in domestic electric circuits.” Justify this statement explaining its role in case of accidental leakage of electric appliances.
    Show answer

    The earth wire gives leakage current a low-resistance path to the earth, so the user is not shocked and the fuse blows.

    The earth wire (green insulation) connects the metal body of an appliance to a metal plate buried deep in the earth, giving a low-resistance conducting path to the earth. If the insulation fails and the live wire touches the metal body (accidental leakage), the leakage current flows through the earth wire into the earth instead of through a person who touches the appliance. This keeps the potential of the body equal to that of the earth, so the user does not get a severe electric shock; the large current that flows also blows the fuse and cuts off the supply. Hence the earth wire is a safety measure, especially for appliances with a metal body such as an electric iron, toaster, table fan or refrigerator.
    Step-by-step solution →
  7. Q33 3 marks

    Also in 31/5/1 (Q33), 31/5/3 (Q28)

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Questions 34–36 · 5 marks each

  1. Q34(a) 5 marks
    Explain chlor-alkali process and write balanced chemical equations for the reactions that occur. Name the gases obtained at the anode and cathode respectively. Mention two uses each of the two gases obtained in the above process.
    Show answer

    Brine electrolysis gives sodium hydroxide, chlorine at the anode and hydrogen at the cathode; chlorine treats drinking water, hydrogen is a fuel.

    Chlor-alkali process: when electricity is passed through brine (a concentrated aqueous solution of sodium chloride), it decomposes to form sodium hydroxide, chlorine and hydrogen; the name comes from chlor (chlorine) and alkali (sodium hydroxide). Overall equation: . At the anode: ; at the cathode: , so sodium hydroxide forms near the cathode. Gas obtained at the anode: chlorine; gas obtained at the cathode: hydrogen. Uses of chlorine: treatment of drinking water and swimming pools; manufacture of PVC, disinfectants, pesticides and bleaching powder. Uses of hydrogen: as a fuel; hydrogenation of vegetable oils to make margarine; manufacture of ammonia for fertilisers.
    Step-by-step solution →
    OR
    Q34(b) 5 marks

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  2. Q35(a) 5 marks

    Also in 31/5/1 (Q36(a))

    1. (i)The potential difference across the two ends of a circuit component is decreased to one-third of its initial value, while its resistance remains constant. What change will be observed in the current flowing through it ? Name and state the law which helps us to answer this question.
    2. (ii)Draw a schematic diagram of a circuit consisting of a battery of four V cells, a resistor, a resistor and a resistor and a plug key, all connected in series. Now find (I) the electric current passing through the circuit, and (II) potential difference across the resistor when the plug key is closed.
    Show answer

    The current falls to one-third (Ohm's law); the circuit current is A and the resistor has V across it.

    (i) The current also decreases to one-third of its initial value, . The law is Ohm's law: the potential difference across the ends of a conductor is directly proportional to the current through it, provided its temperature remains the same; . (ii) Circuit: the four V cells in series (battery of V), the , and resistors and the plug key, all in one loop. (I) A. (II) V.
    Step-by-step solution →
    OR
    Q35(b) 5 marks

    Also in 31/5/1 (Q36(b))

    1. (i)When is the potential difference between two points said to be 1 volt ?
    2. (ii)A copper wire has a diameter of mm and resistivity of . What will be the length of this wire to make its resistance ? How much does the resistance change, if the diameter of the wire is doubled ?
    Show answer

    One volt is 1 J of work per coulomb; the wire is about 27.5 m long; doubling its diameter gives .

    (i) The potential difference between two points is volt when joule of work is done to move a charge of coulomb from one point to the other (). (ii) , so m. If the diameter is doubled, the area becomes times as large, so the resistance becomes one-fourth: , a decrease of .
    Step-by-step solution →
  3. Q36(a) 5 marks

    Also in 31/5/1 (Q35(a)), 31/5/3 (Q34(a))

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    OR
    Q36(b) 5 marks

    Also in 31/5/1 (Q35(b)), 31/5/3 (Q34(b))

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Questions 37–39 · 4 marks each

  1. Q37 4 marks

    Also in 31/5/1 (Q39), 31/5/3 (Q37)

    A highly polished surface such as a mirror reflects most of the light falling on it. In our daily life we use two types of mirrors — plane and spherical. The reflecting surface of a spherical mirrors may be curved inwards or outwards. In concave mirrors, reflection takes place from the inner surface, while in convex mirrors reflection takes place from the outer surface.
    1. (a)Define the principal axis of a concave mirror.[1]
    2. (b)A ray of light is incident on a concave mirror, parallel to its principal axis. If this ray after reflection from the mirror passes through the principal axis from a point at a distance of 10 cm from the pole of the mirror, find the radius of curvature of the mirror.[1]
    3. (c)(i)An object is placed at a distance of 10 cm from the pole of a convex mirror of focal length 15 cm. Find the position of the image.[2]
    4. (c)(ii)OR : A mirror forms a virtual, erect and diminished image of an object. Identify the type of this mirror. Draw a ray diagram to show the image formation in this case.[2]
    Show answer

    The principal axis joins the pole and centre of curvature; cm; cm for the convex mirror; or the mirror is convex.

    (a) The principal axis of a concave mirror is the straight line passing through its pole and its centre of curvature; it is normal to the mirror at the pole. (b) The reflected ray crosses the axis at the principal focus, so cm and cm. (c)(i) With cm and cm, , so cm: the image is formed cm behind the mirror (virtual, erect and diminished, ). (c)(ii) It is a convex mirror. Ray diagram: a ray parallel to the principal axis reflects as if coming from , and a ray directed towards reflects back along itself; their backward extensions meet behind the mirror between and , where the virtual, erect, diminished image is formed.
    Step-by-step solution →
  2. Q38 4 marks

    Also in 31/5/1 (Q37), 31/5/3 (Q38)

    Carbon is a versatile element that forms the basis of all living organisms and many of the things we use. A large variety of compounds is formed because of its tetravalency. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements. Answer the following questions :
    1. (a)What are hydrocarbons ?[1]
    2. (b)List two properties by virtue of which carbon can form a large number of compounds.[1]
    3. (c)(i)Write the formula of the functional group present in (1) aldehydes, and (2) ketones. Write chemical equation for the reaction that occurs between ethanoic acid and ethanol in the presence of a catalyst.[2]
    4. (c)(ii)OR : What are structural isomers ? Write the structures of two isomers of butane ().[2]
    Show answer

    Hydrocarbons contain only carbon and hydrogen; carbon shows catenation and tetravalency; aldehydes have and ketones have .

    (a) Hydrocarbons are compounds of carbon and hydrogen only, for example methane, . (b) Catenation (carbon atoms join with one another into long chains, branched chains and rings) and tetravalency (each carbon atom forms four bonds with carbon or other atoms). (c)(i) (1) Aldehydes: ; (2) Ketones: . Equation: (ethyl ethanoate, an ester). (c)(ii) Structural isomers are compounds with the same molecular formula but different structures. The two isomers of butane are n-butane, , and isobutane, .
    Step-by-step solution →
  3. Q39 4 marks

    Also in 31/5/1 (Q38), 31/5/3 (Q39)

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