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A DNA molecule is 160 base… (Class 12 Biology 2026, Q3)

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BiologyCBSE Class 12 · Board exam 2026, set 57/5/1 · 1 mark · MCQ

CBSE Class 12 Biology 2026: question 3

Set in the CBSE Class 12 board exam of 2026, paper 57/5/1, section A, question 3, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q3 · 1 mark · MCQMolecular Basis of Inheritance

A DNA molecule is 160 base pairs long. It has 30% Guanine. How many Adenine bases are present in this DNA molecule ?

  1. (A)48
  2. (B)64
  3. (C)96
  4. (D)192

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 57/5/1.

Hints

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

Hint 1

How many individual bases are there in 160 base pairs?

Hint 2

G = C and A = T. Find the percentage left for A.

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. 160 base pairs contain bases. By Chargaff's rule G = C = 30%, so A + T = 40% and A = 20%.

    ½ mark

  2. Number of adenine bases . The answer is option (B).

    ½ mark

Answer: 64, option (B)

Where the marks are

  • Uses Chargaff's rule to get A = 20% of 320 bases = 64 (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Molecular Basis of Inheritance, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 57/5/1: 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.