Skip to content

If we make carbon skeleton… (Class 10 Science 2025, Q7)

questionbuddy.in/q/cbse-10-science-2025-31-5-1-q7-make-carbon-skeleton-carbon-atoms

ScienceCBSE Class 10 · Board exam 2025, set 31/5/1 · 1 mark · MCQ

CBSE Class 10 Science 2025: question 7

Set in the CBSE Class 10 board exam of 2025, paper 31/5/1, section A, question 7, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q7 · 1 mark · MCQCarbon and its Compounds

If we make carbon skeleton with four carbon atoms, the two different possible skeletons will be

  1. (A)C–C–C with one C attached below the middle carbon; C–C–C–C
  2. (B)C–C–C–C; C–C(branched) with two C atoms attached to the third carbon (branched skeleton)
  3. (C)C–C–C–C; C–C with a vertical chain of two C atoms attached below the second carbon
  4. (D)C–C–C–C; a ring-shaped skeleton of C atoms with two C atoms attached to the second and third carbons

Figure in the paper: Structural skeleton sketches of carbon chains: option A shows a straight chain C–C–C with a C below the middle carbon, and a straight C–C–C–C chain; option B shows a straight C–C–C–C and a branched skeleton with a C atom attached to the third carbon of a three-carbon chain forming a Y shape; option C shows a straight C–C–C–C and a chain C–C with a vertical arrangement of C atoms below; option D shows a straight C–C–C–C and a skeleton with two C atoms attached to a C–C pair forming a ring-like shape (C–C with C atoms below, C C joined). See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/5/1.

Hints

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

Hint 1

One skeleton is a straight chain.

Hint 2

The other skeleton has a branch. Where can it attach?

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. Four carbon atoms give two skeletons: a straight chain C–C–C–C, and a branched chain made of a three-carbon chain with one carbon attached to the middle carbon.

  2. According to the marking scheme, option (B) shows these two skeletons.

    1 mark

Answer: (B)

Where the marks are

  • Identifies the straight and branched skeletons (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 paper2025 board paper, set 31/5/1: 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.