Although amino acids have "acid" in their name, some are acidic in water solutions, some are basic, and other are neutral. Propose an explanation for this observation

The pH of an amino acid is determined by the nature of the side chains of that amino acid. If the side chain of an amino acid contains amine functional group the amino acid will be basic. The acidic amino acids are acidic because they have carboxylic acid functional groups at their side chain.