Question

carboxylic acid acidity depends on number of carbon atoms present in hydrocarbon chain

Answer 1

Comparing the acidic character between propanoic acid and butanoic acid. In propanoic acid, methyl group is releasing electrons and thus having + I effect on carboxyl group which increases the negative charge on carboxyl ion due to which it will not release protons effectively in comparison to the carboxyl group present in long hydrocarbon chain in which the methyl group is far from carboxyl group and thus having lower + I on carboxyl and the carboxyl group can easily releases proton to show higher acidic character.

Thus with increase in number of carbon atom in hydrocarbon chain, the acidity of carboxyl group increase.