Right choice is (d) Carballylic acid
To elaborate: Malonic acid, glutaric acid and adipic acid are dicarboxylic acids with 3, 5 and 6 carbon atoms in their structures respectively. Carballylic acid, also known as tricarballylic acid is a tricarboxylic acid having 3 carbon atoms excluding the three carboxyl carbons in its structure. Its IUPAC name is Propane-1,2,3-tricarboxylic acid.