Arrange the following three compounds in order of decreasing acidity.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → B > A > C
The three compounds are anilinium ions, the conjugate acids of aniline (A), p-nitroaniline (B) and p-toluidine (C). The weaker the base, the stronger its conjugate acid. Placing each ion, most acidic first:
B (from p-nitroaniline) — first. –\( \ce{NO2} \) is electron withdrawing (−I, −R), so p-nitroaniline is the weakest base and its ion gives up \( \ce{H+} \) most easily.
A (from aniline) — second. No substituent: the reference case.
C (from p-toluidine) — last. –\( \ce{CH3} \) is electron releasing (+I, hyperconjugation), so p-toluidine is the strongest base and its ion holds \( \ce{H+} \) most firmly.
NCERT (2026-27 edition):
Arylamines versus Ammonia – “… In case of substituted aniline, it is observed that electron releasing groups like –OCH3, –CH3 increase basic strength whereas electron withdrawing groups like –NO2, –SO3H, –COOH, –X decrease it.”