Consider the following compounds and arrange them in decreasing order of their acidity.
A.
B.
C.
D.
Choose the correct answer from the option given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C, B, D, A
Electron withdrawing groups raise and electron donating groups lower the acidity of benzoic acid.
So, with benzoic acid as the reference:
two EWG > one EWG > no substituent > EDG
Matching the given compounds:
(C) 2,4-dinitrobenzoic acid: two –\( \ce{NO2} \) groups (pKa about 1.4)
(B) 4-nitrobenzoic acid: one –\( \ce{NO2} \) group (pKa 3.41)
(D) benzoic acid: no substituent (pKa 4.19)
(A) 4-methoxybenzoic acid: electron donating –\( \ce{OCH3} \) group (pKa 4.46)
Shortcut: The dinitro acid (C) must come first. Only Option (2) starts with C.
NCERT (2026-27 edition):
Effect of Substituents on the Acidity of Carboxylic Acids
