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Identify the incorrect… (Class 12 Biology 2025, Q2)

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BiologyCBSE Class 12 · Board exam 2025, set 57/7/1 · 1 mark · MCQ

CBSE Class 12 Biology 2025: question 2

Set in the CBSE Class 12 board exam of 2025, paper 57/7/1, section A, question 2, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q2 · 1 mark · MCQBiotechnology: Principles and Processes

Identify the incorrect statement regarding PCR.

  1. (A)Two sets of primers are required during polymerisation.
  2. (B)The process of replication is repeated multiple times to produce one billion copies.
  3. (C)Thermostable DNA polymerase is used for extension of primers.
  4. (D)Annealing is required to separate both the strands of template DNA.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 57/7/1.

Hints

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

Hint 1

Recall the three steps of PCR in order.

Hint 2

Which step uses high temperature to open the double helix?

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. In PCR the two DNA strands are separated by denaturation at high temperature. Annealing is the step in which primers bind to the single strands.

  2. So the statement in (D) is incorrect.

    1 mark

Answer: (D)

Where the marks are

  • Recognises that strand separation is denaturation, not annealing (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biotechnology: Principles and Processes, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 57/7/1: 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.