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Consider the structures ‘X’… (Class 10 Science 2026, Q20)

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ScienceCBSE Class 10 · Board exam 2026, set 31/3/1 · 1 mark · MCQ

CBSE Class 10 Science 2026: question 20

Set in the CBSE Class 10 board exam of 2026, paper 31/3/1, section B, question 20, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q20 · 1 mark · MCQCarbon and its Compounds

Consider the structures ‘X’ and ‘Y’ given below. Which of the following statements are correct ?

(i) ‘X’ and ‘Y’ are homologues.
(ii) ‘X’ and ‘Y’ have the same structural formula, but different molecular formula.
(iii) ‘X’ and ‘Y’ have the same molecular formula, but different structural formula.
(iv) ‘X’ and ‘Y’ are structural isomers.

  1. (A)(i) and (iii)
  2. (B)(i) and (iv)
  3. (C)(ii) and (iv)
  4. (D)(iii) and (iv)

Figure in the paper: X is the straight-chain four-carbon alkane (n-butane) drawn with all C–H bonds: C–C–C–C in a row. Y is the branched four-carbon alkane (isobutane): a central carbon bonded to three CH3 groups and one H. See it in the official paper.

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 C and H atoms in each structure.

Hint 2

Homologues differ by a –CH unit; do X and Y?

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. Both X and Y are , but X is a straight chain and Y is branched. So they have the same molecular formula with different structures.

  2. Compounds like this are structural isomers, not homologues. So (iii) and (iv) are correct, option (D).

    1 mark

Answer: (D) (iii) and (iv)

Where the marks are

  • Same formula, different structure, so isomers (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.