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Saturday, 31 October

JEE Main 2021 · ChemistryMultiple choiceSingle correctEasyApplication

JEE Main 24 February 2021, Shift 2, Chemistry Q44

Question 44 of 90 in this shift, Chemistry question 14 of 30, Section A.

Which one of the following carbonyl compounds cannot be prepared by addition of water on an alkyne in the presence of HgSO4\mathrm{HgSO_4} and H2SO4\mathrm{H_2SO_4} ?

The figure, in words

Options 1, 2 and 4 are drawn as printed condensed formulas with the C=O drawn above the carbon; option 3 is a drawn six-membered saturated ring bearing a C(=O)-CH3 group.
  1. (1)CH3−C(=O)−H\mathrm{CH_3-C(=O)-H}
  2. (2)CH3−C(=O)−CH2CH3\mathrm{CH_3-C(=O)-CH_2CH_3}
  3. (3)[figure: cyclohexane ring with a C(=O)−CH3\mathrm{C(=O)-CH_3} group attached]
  4. (4)CH3−CH2−C(=O)−H\mathrm{CH_3-CH_2-C(=O)-H}Official answer

Official answer

Option 4

NTA final key.

Chapter
Aldehydes, Ketones and Carboxylic Acids
Topic
Alkenes and Alkynes
Idea tested
Kucherov Alkyne Hydration

Same idea in other shifts

Asked 4× in all
  1. 6 Apr 2026, Shift 2 · Q65An optically active alkyl bromide C4H9Br\mathrm{C_4H_9Br}, reacts with ethanolic KOH to form major compound [A] which reacts with bromine to…MediumSingle correct
  2. 2 Apr 2025, Shift 1 · Q66An optically active alkyl halide C4H9Br\mathrm{C_4H_9Br} [A] reacts with hot KOH dissolved in ethanol and forms alkene [B] as major product…MediumSingle correct
  3. 9 Jan 2020, Shift 1 · Q43The major product (Y) in the following reactions is : CH3−CH(CH3)−C≡CH\mathrm{CH_3-CH(CH_3)-C{\equiv}CH}…MediumDiagram basedHas a figure

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.