Salicylic acid (2-hydroxybenzoic acid) has $p{K}_{a1}=2.97$ for the $\mathrm{COOH}$ and $p{K}_{a2}=13.6$ for the phenolic $\mathrm{OH}$, whereas 4-hydroxybenzoic acid has $p{K}_{a1}=4.54$. A single explanation for both the low $p{K}_{a1}$ and the very high $p{K}_{a2}$ of salicylic acid is

1. Athe $+M$ effect of the ortho $\mathrm{OH}$ group on the carboxylate
2. Bintermolecular hydrogen bonding of salicylic acid with water only
3. Csteric inhibition of resonance in the phenoxide ion
4. Dan intramolecular hydrogen bond between the phenolic $\mathrm{OH}$ and the carboxylate in the monoanion