JEE Main · 2023 · 06 Apr 2023 · Shift 2 · Alcohols Phenols and Ethers

The strength of a phenol as an acid depends on how well the phenoxide ion remaining after deprotonation is stabilised: an electron-withdrawing substituent raises the acidity, while an electron-releasing substituent lowers it. Of the four phenols, the one bearing the nitro group is aided by the strong $-I$ withdrawal of $-\mathrm{N}{\mathrm{O}}_2$, which disperses the negative charge of the phenoxide far more effectively than the weakly withdrawing chlorine. The methyl group releases electrons and makes its phenol even weaker than unsubstituted phenol. The strongest acid is therefore 3-nitrophenol.