Assertion(A) : Acetic acid is stronger acidic than benzoic acid
Reason(R) : As +I or +M effect increases acidic strength decreases

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Both (A) and (R) are true but (R) is not the correct explanation of (A)

(A) false but (R) true

Both (A) and (R) are true and (R) is the correct explanation of (A)

(A) is true but (R) is false

answer is D.

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Detailed Solution

Acidity of carboxylic acids depends on the stability of acid anion. Thus, electron withdrawing group stabilizes anion. Hence, it increases acidity. Similarly, electron donating group destabilizes acid anion and decreases acidity. In acetic acid, -CH₃group decreases acidity as it is an electron donating group. On the other hand, benzoic acid has sp²carbon attached to -COOH group, which is more electronegative than sp³carbon. So, benzene ring with sp²carbon acts as more electron withdrawing group for acid than methyl group in acetic acid. Hence, benzoic acid is more acidic than acetic acid.

+I effect decreases the acidic strength of carboxylic acids due to +I groups like alkyl groups.

Acidic strength is directly proportional to the -M effect.
Acidic strength is directly proportional to the -I effect.
Acidic strength is indirectly proportional to the +M effect.
Acidic strength is indirectly proportional to the +I effect.

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