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JEE Main levelSingle correct optionDifficulty 2 of 3co265

The acid shown has $p K_{a} = 4.47$ , while benzoic acid has $p K_{a} = 4.20$ . The best explanation is

AThe -I effect of oxygen stabilises the carboxylate, so it should be stronger, which contradicts the data
BThe +R effect of the para methoxy group donates electron density to the ring and destabilises the carboxylate, so it is a weaker acid
CResonance donation by OMe stabilises the carboxylate and strengthens the acid
DPara substituents never influence acidity

Answer: B

The drawn compound is 4-methoxybenzoic acid. At the para position the +R effect of OCH3 outweighs its -I effect, raising electron density at the carboxylate carbon and destabilising the anion, giving pKa 4.47 > 4.20.

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