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Answer the following. (Science 2026 31/3/1 Q29a)

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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(a)

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

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

Answer the following.

  1. (i)

    What is homologous series ? Which two of the following organic compounds belong to the same homologous series ?
    , , ,

    2 marks
  2. (ii)

    Write the product(s) in the following reactions :
    (I)
    (II)

    2 marks
  3. (iii)

    Why does micelle formation take place when soap is added to water ?

    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

Check each formula against CₙH₂ₙ₊₂, CₙH₂ₙ and CₙH₂ₙ₋₂.

Hint 2

An alcohol and an acid with an acid catalyst give an ester. For soap, think of the two ends of the molecule and which one likes water.

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) A homologous series is a series of compounds in which the same functional group replaces hydrogen in a carbon chain. Members have the same general formula, and successive members differ by a unit (14 u).

    1 mark

  2. and belong to the same homologous series. Both fit (alkenes), whereas is an alkane and is an alkyne.

    1 mark

  3. (ii)(I) Esterification: (products: ethyl ethanoate, an ester, and water).

    1 mark

  4. (ii)(II) Combustion: (with heat and light).

    1 mark

  5. (iii) A soap molecule has an ionic (hydrophilic) end that interacts with water and a long hydrocarbon (hydrophobic) tail that avoids water and interacts with oil or dirt. In water, the molecules therefore cluster with their tails pointing inward and their ionic ends facing outward towards the water. This cluster is a micelle, and it traps oily dirt at its centre.

    1 mark

Answer: (i) Series with the same functional group/general formula, successive members differing by CH₂; C₂H₄ and C₄H₈. (ii)(I) CH₃COOC₂H₅ + H₂O; (II) 2CO₂ + 3H₂O. (iii) The ionic end faces water and the hydrocarbon tail faces oil, so a micelle forms.

Where the marks are

  • Definition of homologous series (1 mark)
  • Identifies C₂H₄ and C₄H₈ (1 mark)
  • Ester and water as products of (I) (1 mark)
  • CO₂ and H₂O as products of (II) (1 mark)
  • Explains micelle formation through the ionic end and the hydrocarbon tail (1 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.