Acidity 2

Because of Benzoic Acid is less Acidic than the other, 2,6-Dihydroxy Benzoic Acid is most likely to choose

Due to increased stability after removal of hydrogen from COOH group .... because of hydrogen bonding

$Explanation$ : when the hydrogen leaves from all .., the maximum stability is gained by 2,6dihydroxybenzoicacid because of two hydroxy group stabilising the ion formed by hydrogen bonding which stabilises the charge of the ion.

$Information$ : Don't consider the ortho effect here ...The OH group is not capable of providing stearic hindrance which provides the ortho effect

This can also be explained with the help of 'Ortho Effect'... While all substituents on aryl rings can influence acidity by inductive and mesomeric effects, substituents on the ortho position are special. They can also influence acidity significantly by sterics, forcing the carboxylic acid group to bend out of the plane of the benzene ring. Since conjugation of carboxylic acid to aryl rings is known to increase the its acidity, bending out of the plane causes an acidity decrease. More poorly understood but also thought to be significant is that ortho substituents can inhibit solvation of the carboxylate anion.....