in general, acids have greater tendency to loose $H^+$ compared to alcohols.
Out of III and IV , III is stronger acid tahn $IV$ due to the presence of $CH_3$ (+I effect) which makes the release of proton difficult from the latter.
Out of I and II ,II is a stronger acid due to presence of Cl(-I effect) which facilitates the release of proton than by (I).
Hence the order is $ III > IV > II > I$
Hence a is the correct answer.