ChemistryCBSE Class 12 · Sample paper, session 2026-27 · 1 mark · MCQ

CBSE Class 12 Chemistry sample paper 2026-27: question 8

From the official CBSE sample question paper for 2026-27, section A, question 8, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q8 · 1 mark · MCQAldehydes, Ketones and Carboxylic Acids

Identify the Grignard reagent and carbonyl compound which on reaction followed by hydrolysis will give 3-methyl pentan-3-ol.

(i) $C_{2} H_{5} C O C_{2} H_{5} + C H_{3} M g C l$ (ii) $C_{2} H_{5} C O C H_{3} + C_{2} H_{5} M g C l$
(iii) $C H_{3} C H O + C_{2} H_{5} - C H (M g C l) - C_{2} H_{5}$ (iv) $C_{2} H_{5} C H O + C H_{3} - C H (M g C l) - C_{2} H_{5}$

(A)(i) and (iii)
(B)(ii) and (iv)
(C)(iii) and (iv)
(D)(i) and (ii)

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

Draw the structure of 3-methylpentan-3-ol and classify the alcohol.

Hint 2

Recall that aldehydes give secondary alcohols with Grignard reagents.

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.

3-Methylpentan-3-ol is $(C_{2} H_{5})_{2} C (O H) C H_{3}$ , a tertiary alcohol, so it must come from a ketone and a Grignard reagent.
(i) $C_{2} H_{5} C O C_{2} H_{5} + C H_{3} M g C l$ and (ii) $C_{2} H_{5} C O C H_{3} + C_{2} H_{5} M g C l$ both give $(C_{2} H_{5})_{2} C (O H) C H_{3}$ after hydrolysis. Options (iii) and (iv) use aldehydes, which give secondary alcohols. So the answer is D.
1 mark

Answer: Option (D) (i) and (ii)

Where the marks are

Recognises a tertiary alcohol needs ketone + RMgX; selects (i) and (ii) (1 mark)

Revise the chapter

Chapter: Aldehydes, Ketones and Carboxylic Acids (notes, formulas, where marks are lost and every past question)

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 2026-27: every question, by section.

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CBSE Class 12 Chemistry sample paper 2026-27: question 8

Hints

Step-by-step solution

Revise the chapter

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