Skip to content

Answer the following. (Class 12 Chemistry 2025, Q32a)

questionbuddy.in/q/cbse-12-chemistry-2025-56-7-1-q32a

ChemistryCBSE Class 12 · Board exam 2025, set 56/7/1 · 5 marks · Long answer

CBSE Class 12 Chemistry 2025: question 32(a)

Set in the CBSE Class 12 board exam of 2025, paper 56/7/1, section E, question 32(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q32(a) · 5 marks · Long answerAldehydes, Ketones and Carboxylic Acids

Answer the following.

  1. (i)

    An organic compound (X) having molecular formula can show various properties depending on its structures. Draw each of the structures if it : (I) shows Cannizzaro reaction. (II) reduces Tollens’ reagent and has a chiral carbon. (III) gives positive iodoform test.

    3 marks
  2. (ii)

    Write the reaction involved in the following : (I) Clemmensen reduction (II) Etard reaction

    2 marks

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

Cannizzaro needs an aldehyde with no α-hydrogen.

Hint 2

A chiral carbon has four different groups; the iodoform test needs a CH₃CO– group.

Hint 3

Clemmensen uses zinc amalgam and HCl; Etard uses chromyl chloride on toluene.

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. (i)(I) To show the Cannizzaro reaction, the aldehyde must have no α-H: , 2,2-dimethylpropanal.

    1 mark

  2. (i)(II) To reduce Tollens' reagent it must be an aldehyde, and it must also have a chiral carbon: , 2-methylbutanal. C-2 carries H, CH₃, C₂H₅ and CHO.

    1 mark

  3. (i)(III) To give a positive iodoform test it must be a methyl ketone: , pentan-2-one. 3-Methylbutan-2-one is also acceptable.

    1 mark

  4. (ii)(I) Clemmensen reduction: the carbonyl group is reduced to .

    1 mark

  5. (ii)(II) Etard reaction: toluene is oxidised to benzaldehyde by chromyl chloride.

    1 mark

Answer: (i) (I) (CH₃)₃C–CHO; (II) CH₃CH₂CH(CH₃)CHO; (III) CH₃COCH₂CH₂CH₃. (ii) Clemmensen: >C=O → >CH₂ with Zn-Hg/HCl; Etard: toluene → benzaldehyde with CrO₂Cl₂.

Where the marks are

  • 2,2-Dimethylpropanal (1 mark)
  • 2-Methylbutanal (1 mark)
  • Pentan-2-one (1 mark)
  • Clemmensen reduction equation (1 mark)
  • Etard reaction equation (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Aldehydes, Ketones and Carboxylic Acids, 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.