Among the following compounds, the most acidic is
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IIT-JEE 2011 · Paper 1, Chemistry question 6
Answer and worked solution
Official answer: C
pKa values: o-hydroxybenzoic (salicylic) acid ≈ 3.0, p-hydroxybenzoic acid ≈ 4.5, p-toluic acid ≈ 4.4, p-nitrophenol ≈ 7.2.
Salicylic acid is the strongest: its carboxylate is stabilised by an intramolecular hydrogen bond with the ortho OH.
(C)