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Answer the following. (Science 2025 31/2/1 Q22)

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ScienceCBSE Class 10 · Board exam 2025, set 31/2/1 · 2 marks · Very short answer

CBSE Class 10 Science 2025: question 22

Set in the CBSE Class 10 board exam of 2025, paper 31/2/1, section B, question 22, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q22 · 2 marks · Very short answerCarbon and its Compounds

Answer the following.

  1. (a)

    Select from the following the members of same homologous series: (1) with all H's (aldehyde/ketone-type chain as printed: CH3–CH2–CHO type); (2) with all H's; (3) with all H's; (4) with all H's, as printed in the structures below.

    0 marks
  2. (b)

    What happens to (i) the melting point, and (ii) the solubility of compounds as the molecular mass of the compounds in a homologous series increases?

    0 marks

Figure in the paper: Four structural formulas labelled (1) to (4). (1): three carbons in a chain, the last carbon double bonded to O (aldehyde), all other valences filled with H. (2): three carbons, with a C=O (ketone) at the middle carbon, all valences filled with H. (3): three carbons, last carbon double bonded to O and bonded to OH (carboxylic acid). (4): four carbons in a chain, last carbon double bonded to O, all valences filled with H. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/2/1.

Hints

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

Hint 1

First identify the functional group in each structure.

Hint 2

Physical properties change step by step as the chain gets longer.

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. (a) Members of a homologous series have the same functional group and differ by one unit.

    • (1) is propanal, (aldehyde)
    • (4) is butanal, (aldehyde)
    • (2) is propanone (ketone) and (3) is propanoic acid (carboxylic acid)

    So (1) and (4) are in the same series; they differ by one .

    1 mark

  2. (b)(i) As molecular mass increases along the series, the melting point increases gradually.

    ½ mark

  3. (b)(ii) Solubility changes gradually. In a given solvent such as water, it decreases as molecular mass increases. Chemical properties stay similar because they depend on the functional group.

    ½ mark

Answer: (a) (1) and (4); (b)(i) melting point increases; (ii) solubility shows gradation (decreases)

Where the marks are

  • Selects (1) and (4) as the same homologous series (1 mark)
  • States that melting point increases with molecular mass (½ mark)
  • States that solubility shows gradation / decreases (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 paper2025 board paper, set 31/2/1: 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.