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Write the reactions… (Class 12 Chemistry 2025, Q21)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/1/1 · 2 marks · Very short answer

CBSE Class 12 Chemistry 2025: question 21

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section B, question 21, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q21 · 2 marks · Very short answerBiomolecules

Write the reactions involved when D-glucose is treated with the following reagents : (1 + 1 = 2)
(a) HCN
(b) water

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

Glucose contains a free aldehyde group in its open-chain form.

Hint 2

HCN adds to C=O; bromine water is a mild oxidant that attacks only –CHO.

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. (a) HCN adds across the aldehyde group of glucose to form glucose cyanohydrin:

    1 mark

  2. (b) Bromine water, a mild oxidising agent, oxidises the –CHO group to –COOH and gives gluconic acid:

    1 mark

Answer: (a) Glucose cyanohydrin; (b) Gluconic acid

Where the marks are

  • Correct reaction forming the cyanohydrin (1 mark)
  • Correct reaction forming gluconic acid (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.