Among the following hydrogens which one is the most acidic?

The correct answer is Option (3) → H_c

Hydrogen H_c is on the \( \ce{CH2} \) group lying between the benzene ring and the carbonyl group. When this proton is removed, the negative charge of the carbanion is spread over the C=O group (enolate) and also into the benzene ring, so this anion is the most stable and H_c is the most acidic.

Why the other options are incorrect

• Option (1) H_a — Incorrect. The hydrogens of the terminal \( \ce{CH3} \) are not on a carbon next to C=O (they are β-hydrogens), so their anion has no resonance stabilisation.

• Option (2) H_b — Incorrect. This \( \ce{CH2} \) is α to the carbonyl, so it is acidic, but its anion is stabilised by the C=O group only; it is less acidic than H_c.

• Option (4) H_d — Incorrect. A hydrogen on the benzene ring (sp² C–H) is very weakly acidic; its anion cannot be delocalised.

NCERT (2026-27 edition):
Reactions due to α-Hydrogen – …