Question

The most acidic among the following is

• A. $p$-cresol
• B. $o$-cresol
• C. $p$-nitrophenol
• D. $p$-chlorophenol

Answer 1

Answer: (C)

$p$-nitrophenol

Answer 2

Presence of electron withdrawing substitutent (like $-NO_{2},-Cl$ ) stabilises the phenoxide ion more by dispersal, of negative charge, thus increases the acidity of phenol. While electron releasing groups (like $-CH_{3},-OCH_{3}$ etc) destabilises the phenoxide ion by intensifying the negative charge and thus, decreases the acidity of phenol. Electron withdrawing power of nitro group is more than the chloro group. Hence, $p$-nitro phenol is most acidic among the given.