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A + B dil NaOH… (Class 12 Chemistry SQP 2023-24, Q2)

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ChemistryCBSE Class 12 · Sample paper, session 2023-24 · 1 mark · MCQ

CBSE Class 12 Chemistry sample paper 2023-24: question 2

From the official CBSE sample question paper for 2023-24, section A, question 2, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q2 · 1 mark · MCQAldehydes, Ketones and Carboxylic Acids

product shown. Identify A and B:

  1. (A)A = 1-phenylethanal, B = acetophenone
  2. (B)A = Benzophenone, B = formaldehyde
  3. (C)A = Benzaldehyde, B = Acetophenone
  4. (D)A = Benzophenone, B = Acetophenone

Figure in the paper: Product is chalcone: two benzene rings joined by the chain -CH=CH-C(=O)-, i.e. C6H5-CH=CH-CO-C6H5. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Split the product at the C=C double bond.

Hint 2

One part comes from an aldehyde with no α-H and the other from a methyl ketone.

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. Chalcone is formed by crossed aldol condensation.

  2. (no α-H) reacts with the enolate of ; the aldol then loses water to give chalcone. So A = benzaldehyde and B = acetophenone.

    1 mark

Answer: (C) Benzaldehyde and Acetophenone

Where the marks are

  • Identifies a crossed aldol between benzaldehyde and acetophenone (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 paperSample paper 2023-24: 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.