Dissociation constant of benzoic acid, `p-`nitro benzoic acid and `p-`hydroxy benzoic acid are `6.3 xx 10^(-5), 36 xx 10^(-5) " and ", 2.5 xx 10^(-5)` respectively. Explain

Explanation

(i) `NO_(2)` group is an electron withdrawing group and tends to stabilise the carboxylate anion more than the benzoate ion after the release of `H^(+)` ion. Thus, `p-`nitrobenzoic acid is a stronger acid than benzoic acid.
(ii) OH group is an electron releasing group and tends to destabilise the carboxylate anion more than the benzoate ion after the release of `H^(+)`ion. Thus, `p-`hydroxybenzoic acid is a weaker acid than benzoic acid.
The relative order of acidic strengths is, thus, justified