Arrange the following carboxylic acids in increasing order of their a…

The correct answer is Option (3) → D > C > A > B

The strength of a carboxylic acid depends on the stability of its carboxylate ion. Electron-withdrawing groups spread the negative charge and increase acidity; electron-releasing alkyl groups concentrate it and decrease acidity. A phenyl group is electron-withdrawing (sp² carbon), and its effect weakens as it moves away from –COOH.

• D. C₆H₅COOH — phenyl directly on –COOH: strongest (pK_a 4.19).

• C. C₆H₅CH₂COOH — phenyl one \( \ce{CH2} \) away: weaker effect (pK_a 4.31).

• A. CH₃COOH — one electron-releasing \( \ce{CH3} \) group (pK_a 4.76).

• B. CH₃CH₂COOH — the larger ethyl group releases more electron density: weakest (pK_a 4.88).

Shortcut: benzoic acid (D) is the strongest and propanoic acid (B) the weakest of the four; only Option (3) places D and B at the two ends.

Note: It seems that there is a mistake in the original NTA paper, which asks for the increasing order of acid strength when every option is printed with > signs (a decreasing order).

NCERT (2026-27 edition):
Effect of Substituents on the Acidity of Carboxylic Acids – …