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Identify A and B in each of… (Class 12 Chemistry 2025, Q20)

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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 20

Set in the CBSE Class 12 board exam of 2025, paper 56/1/1, section B, question 20, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q20 · 2 marks · Very short answerAmines

Identify A and B in each of the following reaction sequence : (1 + 1 = 2)
(a)
(b)

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

CN⁻ is a nucleophile, and H₂/Ni reduces a nitrile.

Hint 2

NaNO₂/HCl at 0–5 °C acting on a primary aromatic amine gives a diazonium salt.

Hint 3

A diazonium salt couples with aniline at the para position to form an azo compound.

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) Cyanide ion replaces Cl by nucleophilic substitution: A = (propanenitrile).

    ½ mark

  2. reduces to : B = (propan-1-amine).

    ½ mark

  3. (b) Diazotisation of aniline at 0–5 °C gives A = (benzenediazonium chloride).

    ½ mark

  4. Coupling with aniline in acidic medium at the para position gives B = (p-aminoazobenzene, a yellow dye).

    ½ mark

Answer: (a) A = CH₃CH₂CN, B = CH₃CH₂CH₂NH₂; (b) A = C₆H₅N₂⁺Cl⁻, B = p-aminoazobenzene

Where the marks are

  • A = CH₃CH₂CN (½ mark)
  • B = CH₃CH₂CH₂NH₂ (½ mark)
  • A = benzenediazonium chloride (½ mark)
  • B = p-aminoazobenzene (½ mark)

Revise the chapter

  • Chapter: Amines (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Amines, 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.