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Which of the following substituted phenols is the strongest acid?
A
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B
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C
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D
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Detailed Solution
Electron-withdrawing groups (like $-NO_2$) stabilise the phenoxide ion by delocalising the negative charge (through resonance and inductive effect), increasing acidity. Electron-donating groups ($-CH_3$, $-OCH_3$, $-C_2H_5$) destabilise the phenoxide ion, decreasing acidity. So p-nitrophenol, with the strong EWG $-NO_2$, is the strongest acid among the given options.