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A compound (A) with… (Class 12 Chemistry 2025, Q25)

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

CBSE Class 12 Chemistry 2025: question 25

Set in the CBSE Class 12 board exam of 2025, paper 56/7/1, section C, question 25, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q25 · 3 marks · Short answerHaloalkanes and Haloarenes

A compound (A) with molecular formula which is a primary alkyl halide, reacts with alcoholic KOH to give compound (B). Compound (B) reacts with HI to give (C) which is an isomer of (A). When (A) reacts with Na metal in the presence of dry ether, it gives a compound (D), , which is different from the compound formed when n-butyl iodide reacts with sodium. Write the structures of (A), (B), (C) and (D). Write the chemical equation when compound (A) is reacted with alcoholic KOH.

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

There are only two primary iodides with formula ; one of them is n-butyl iodide.

Hint 2

Alcoholic KOH removes HX to form an alkene; HI then adds by Markovnikov's rule.

Hint 3

In the Wurtz reaction, two alkyl groups join together.

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): , 1-iodo-2-methylpropane (isobutyl iodide). It is a primary iodide, and its Wurtz product is not n-octane.

    ½ mark

  2. (B): , 2-methylpropene.

    ½ mark

  3. (C): , 2-iodo-2-methylpropane. It forms by Markovnikov addition of HI and is an isomer of A.

    ½ mark

  4. (D): , 2,5-dimethylhexane, . It forms by the Wurtz reaction: .

    ½ mark

  5. Reaction of A with alcoholic KOH (dehydrohalogenation):

    1 mark

Answer: A = (CH₃)₂CHCH₂I; B = (CH₃)₂C=CH₂; C = (CH₃)₃CI; D = (CH₃)₂CHCH₂CH₂CH(CH₃)₂

Where the marks are

  • Structure of A (½ mark)
  • Structure of B (½ mark)
  • Structure of C (½ mark)
  • Structure of D (½ mark)
  • Equation of A with alcoholic KOH (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Haloalkanes and Haloarenes, 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.