Which of the following would be expected to be the most highly ionized in water ?

-I effect groups increases the acidity of carboxylic acid and +I effect group decreases the acidity of carboxylic acid. In option (c), the carbon atom that has carboxylic group has two chlorine atoms which is a strong electron withdrawing group and helps to remove the hydrogen from the compound most easily. In option (b), the chlorine atom is one beta carbon atom due to which the strength of the inductive effect decreases.