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The ascending acidity order of the following H atoms is HC≡C—H H2C=CH—H H3C—C(H)(H)(H)—H H3C—CH2—H A B C D

1. D < C < B < A
2. A < B < C < D
3. C < D < B < A
4. A < B < D < C

Correct answer: C < D < B < A

Solution

The correct order reflects the increasing acidity of the hydrogen atoms based on their hybridization and the stability of the resulting conjugate bases. Terminal alkynes (HC≡C—H) are more acidic than alkenes (H2C=CH—H), which are more acidic than alkanes (H3C—C(H)(H)(H)—H and H3C—CH2—H) due to the greater s-character in the sp hybridized carbon of the alkyne, leading to a more stable conjugate base.

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