Explanation

(c)
A monosubstituted benzoic acid is stronger than a monosubstituted phenol as former being a carboxylic acid. Among the given substituted benzoic acid, $ortho -$ hydroxy acid is strongest acid although – OH causes electron donation by resonance effect which tends to decreases acid strength. It is due to very high stabilisation of conjugate base by intramolecular H-bond which outweight the electron donating resonance effect of – OH.
[image:12_image267.emf]
The overall order of acid-strength of given four acids is $ortho$-hydroxybenzoic acid $\left( pK_{a} = 2.98 \right) >$ Toluic acid $pk_{a} = 4.37) > p -$hydroxybenzoic acid
$\left( pk_{a} = 4.58 \right) > p -$nitrophenol $(pk_{a} = 7.15)$.