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Write the reaction of… (Class 12 Chemistry 2025, Q28)

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ChemistryCBSE Class 12 · Board exam 2025, set 56/7/1 · 3 marks · Short answer

CBSE Class 12 Chemistry 2025: question 28

Set in the CBSE Class 12 board exam of 2025, paper 56/7/1, section C, question 28, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q28 · 3 marks · Short answerBiomolecules

Write the reaction of D-Glucose with the following :

  1. (a)

    HCN

    1 mark
  2. (b)

    water

    1 mark
  3. (c)

    1 mark

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 56/7/1.

Hints

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

Hint 1

HCN adds across a carbonyl group.

Hint 2

Bromine water is a mild oxidising agent that attacks only the aldehyde group.

Hint 3

Acetic anhydride acetylates every –OH group; count how many glucose has.

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) Glucose forms a cyanohydrin at the –CHO group:
    (glucose cyanohydrin)

    1 mark

  2. (b) Bromine water, a mild oxidant, oxidises –CHO to –COOH:
    (gluconic acid)

    1 mark

  3. (c) Acetylation of all five –OH groups:
    (glucose pentaacetate)

    1 mark

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

Where the marks are

  • Correct cyanohydrin equation (1 mark)
  • Correct gluconic acid equation (1 mark)
  • Correct pentaacetate equation (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 56/7/1: 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.