Chemistry - GOC Question with Solution | TestHub

A meta $\mathrm{OH}$ group withdraws by induction only (no resonance path to COOH), so 3-hydroxybenzoic acid (b) is slightly stronger than benzoic acid (c) ($\mathrm{p}{K}_{\mathrm{a}}$ 4.08 vs 4.20). A para $\mathrm{OH}$ donates electron density by resonance toward the COOH group and destabilises the carboxylate, making 4-hydroxybenzoic acid (a) the weakest ($\mathrm{p}{K}_{\mathrm{a}}$ 4.58). Hence b $>$ c $>$ a.