The correct order of acid character of the following compounds is :

Solution

Chemistry ma’am · 3 steps

First split by group: every COOH beats phenol. Then rank the three acids by what sits para to COOH.

1. Acid group first. In a carboxylate ion the negative charge is shared equally between two oxygen atoms. In phenoxide it is pushed onto ring carbons, which hold it less well. So phenol (I) is the weakest acid here.
2. Then the substituent. Among the three benzoic acids, a group that pulls electrons away stabilises the carboxylate and raises acidity. A group that pushes electrons in destabilises it and lowers acidity.

   Compound	Para group and its effect	Approx. pKₐ
   II, p-nitrobenzoic acid	-NO₂, strong -I and -M, withdraws	3.4
   III, benzoic acid	none, the reference	4.2
   IV, p-toluic acid	-CH₃, +I and hyperconjugation, donates	4.4
   I, phenol	-OH instead of -COOH	10

3. So. A lower pKₐ means a stronger acid, so the order is II > III > IV > I, which is option (c).

The idea to keep. To rank acids, compare the type of acidic group first, then the substituents. Electron-withdrawing groups stabilise the anion and raise acidity, while electron-donating groups lower it.

Answer from the NTA final answer key. Solution by PrepWiser.