Arrange the following compounds in increasing order of their acidic strength?

Choose the correct answer from the options given below:

(C), (B), (D), (A)

The correct answer is Option (1) → (C), (B), (D), (A)

Core Concept

Acidity of substituted benzoic acids depends on the electron-withdrawing or electron-donating nature of substituents.

Electron-withdrawing groups increase acidity by stabilizing the carboxylate ion.

Electron-donating groups decrease acidity by destabilizing the carboxylate ion.

Explanation

(A) p-NO₂ (Strong Electron Withdrawing Group)

NO₂ shows strong –I and –R effect.

It stabilizes the carboxylate ion significantly.

Hence, it increases acidity the most.

(B) p-NH₂ (Strong Electron Donating Group)

NH₂ shows +R effect.

It pushes electron density towards the ring.

This destabilizes the carboxylate ion.

Hence, least acidic.

(C) p-CH₃ (Weak Electron Donating Group)

CH₃ shows +I effect.

It slightly donates electron density.

So acidity decreases but less than NH₂.

(D) p-Cl (Electron Withdrawing by –I, donating by +R)

Net effect is electron withdrawing due to strong –I.

So acidity increases but less than NO₂.