Among the following compounds, the most acidic is

Step-by-step solution

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 cause electron donation by resonance effect which tends to decrease acid strength. It is due to a very high stabilization of conjugate base by intramolecular H -bond which outweight the electron donating resonance effect of - OH . The overall order of acid-strength of given four acids is ortho-hydro x y benzoic acid (