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Assertion (A) : All… (Class 12 Chemistry 2025, Q16)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/1/1 · 1 mark · Assertion-reason

CBSE Class 12 Chemistry 2025: question 16

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section A, question 16, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q16 · 1 mark · Assertion-reasonCompetency-basedBiomolecules

Assertion (A) : All naturally occurring -amino acids except glycine are optically active.
Reason (R) : Most naturally occurring amino acids have L-configuration.

  1. (A)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
  2. (B)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
  3. (C)Assertion (A) is true, but Reason (R) is false.
  4. (D)Assertion (A) is false, but Reason (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 56/1/1.

Hints

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

Hint 1

Why is glycine optically inactive?

Hint 2

Does L/D configuration cause optical activity?

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. Every α-amino acid except glycine has a chiral α-carbon, so A is true. Most natural amino acids are L-configured, so R is also true.

  2. Optical activity comes from chirality, not from the L-configuration, so R does not explain A. The answer is option (B).

    1 mark

Answer: Option (B)

Where the marks are

  • Recognises both are true but R is not the explanation (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biomolecules, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 56/1/1: 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.