Ease Into Prep with an MCAT^® Question of the Day

B is the correct answer.

The acidity of carboxylic acids is significantly increased by the presence of highly electronegative functional groups. Their electron-withdrawing effect increases the stability of the carboxylate anion, favoring proton dissociation. This effect increases as the number of electronegative groups on the chain increases, and it also increases as the distance between the acid functionality and electronegative group decreases. This answer has two halogens bound to it, at a smaller distance from the carboxyl group compared to the other answers.