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Answer the following. (Science 2026 31/3/1 Q29b)

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ScienceCBSE Class 10 · Board exam 2026, set 31/3/1 · 5 marks · Long answer

CBSE Class 10 Science 2026: question 29(b)

Set in the CBSE Class 10 board exam of 2026, paper 31/3/1, section B, question 29(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q29(b) · 5 marks · Long answerCarbon and its Compounds

Answer the following.

  1. (i)

    Name the following compounds :
    (I) (a carbon doubly bonded to O, between two groups)
    (II) (drawn with H atoms above and below the first carbon)

    1 mark
  2. (ii)

    Name the reaction which is commonly used in the conversion of vegetable oils to fats.

    1 mark
  3. (iii)

    Why is the melting point of higher than ?

    1 mark
  4. (iv)

    What happens when a piece of sodium is dropped into ethanol ?

    1 mark
  5. (v)

    Write the products in the following reaction :

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/3/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Count the carbons and identify the functional group: a C=O in the middle of the chain, and a triple bond.

Hint 2

Oils become fats by adding hydrogen. An ester breaks down with an alkali to give back the alcohol and a salt of the acid.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i)(I) is propanone (acetone), a ketone with 3 carbon atoms.

    ½ mark

  2. (i)(II) is propyne, an alkyne with 3 carbon atoms.

    ½ mark

  3. (ii) Hydrogenation, an addition reaction: hydrogen is added to unsaturated vegetable oils in the presence of a nickel catalyst, converting them into saturated fats.

    1 mark

  4. (iii) (butane, 58 u) has a higher molecular mass than (propane, 44 u). In a homologous series, melting point increases with increasing molecular mass, so butane has the higher melting point.

    1 mark

  5. (iv) Sodium reacts with ethanol to form sodium ethoxide, and hydrogen gas is evolved with effervescence:

    1 mark

  6. (v) Saponification: . The products are sodium ethanoate and ethanol.

    1 mark

Answer: (i) Propanone, Propyne; (ii) Hydrogenation (addition); (iii) Higher molecular mass; (iv) Sodium ethoxide + H₂ gas; (v) CH₃COONa + C₂H₅OH

Where the marks are

  • Propanone (½ mark); Propyne (½ mark)
  • Hydrogenation / addition reaction (1 mark)
  • Higher molecular mass gives higher melting point (1 mark)
  • Sodium ethoxide and hydrogen gas formed (1 mark)
  • Sodium ethanoate (½ mark) and ethanol (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Carbon and its Compounds, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/3/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.