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Chlorobenzene can be… (Class 12 Chemistry SQP 2026-27, Q20)

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ChemistryCBSE Class 12 · Sample paper, session 2026-27 · 2 marks · Very short answer

CBSE Class 12 Chemistry sample paper 2026-27: question 20

From the official CBSE sample question paper for 2026-27, 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 answerHaloalkanes and Haloarenes

Chlorobenzene can be converted into phenol by heating in aqueous sodium hydroxide solution at a temperature of 623K and 300 atm, however presence of a substituent group effects its activity towards this nucleophilic substitution reaction.

Which substituent (i) nitro or (ii) methoxy will increase the reactivity of chlorobenzene and why?

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

Nucleophilic attack is easier when the ring is electron-poor.

Hint 2

Which group withdraws electrons, and which donates them by resonance?

Hint 3

Think about the stability of the negatively charged intermediate.

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. The nitro group increases the reactivity of chlorobenzene towards nucleophilic substitution.

    1 mark

  2. is strongly electron-withdrawing (–I and –R effects). It lowers the electron density of the ring and favours attack by . The methoxy group is electron-donating (+R), so it does the opposite.

    ½ mark

  3. With at the ortho or para position, the negative charge of the carbanion (σ-complex) formed after attacks is delocalised onto the nitro group by resonance. This stabilises the intermediate, so substitution occurs readily (even at much milder conditions).

    ½ mark

Answer: (i) Nitro, because its –I/–R effect withdraws electrons and stabilises the carbanion intermediate at o/p positions.

Where the marks are

  • Identifies the nitro group (1 mark)
  • Electron-withdrawing –I/–R nature of nitro versus electron-donating methoxy (½ mark)
  • Resonance stabilisation of the negative charge of the intermediate at o/p positions (½ 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 paperSample paper 2026-27: 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.