The correct order of strengths of the carboxylic acids

Presence of electron withdrawing group increases the acidic strength of carboxylic acid. So in option (II) and (III) the oxygen (electron withdrawing) makes it more acidic, but presence of oxygen in (II) is near to carboxylic group which makes it more acidic than (III) as it contains oxygen a bit away from the carboxylic group. The correct order of acidity is II>III>I. Hence, option D is correct.