To solve this problem, we need to understand why carboxylic acids have higher boiling points compared to aldehydes, ketones, and alcohols of similar molecular mass.$\newline$The key reason is the formation of intermolecular hydrogen bonds.$\newline$Let's analyze the options:$\newline$• Option 1: More extensive association via van der Waals force of attraction.$\newline$ This is incorrect because van der Waals forces are weaker compared to hydrogen bonding.$\newline$• Option 2: Formation of carboxylate ion.$\newline$ This is incorrect because carboxylate ions are formed in the ionization of carboxylic acids, not in their boiling process.$\newline$• Option 3: Formation of intramolecular H-bonding.$\newline$ This is incorrect because intramolecular hydrogen bonding occurs within a molecule, not between molecules.$\newline$• Option 4: Formation of intermolecular H-bonding.$\newline$ This is correct. Carboxylic acids can form strong intermolecular hydrogen bonds, leading to dimerization.$\newline$ This dimerization increases the effective molecular size and the boiling point.$\newline$Therefore, the correct option is Option 4: Formation of intermolecular H-bonding.