The correct order of acidity for following compounds is

Answer

A

Explanation

We know that the strength of an acid depends upon the stability of its carboxylate anion. Greater the stability of the carboxylate anion more acidic is the carboxylic acid. Now the carboxylate ion from 2,6-dihydroxybenzoic acid (I) is more stable due to chelation with two OH groups than anion of salicylic acid which is stabilized by chelation with only one OH group.

Further, OH group has a strong +R-efect and a weak -I-effect. since at m-position OH group cannot exert its +R-effect but can only exert its -I-effect, therefore, m-hydroxybenzoic acid (III) is a stronger acid than p-hydroxybenzoic acid (IV) where OH group exerts its strong +R-effect as shown

thus, the overall acid strength decreases in the order:
`underset((pK_(a)=4.08))("2,6-Dihydroxybenzoic acid (I)") gt underset((pK_(a)=2.98))("Salicyclic acid (II)")gt underset((pK_(a)=4.08))("m-Hydroxybenzoic acid (III)") gt underset((pK_(a)=4.58))("p-Hydroxybenzoic (IV)")`