Amino acids contain both an acidic carboxyl group ($-\text{COOH}$) and a basic amino group ($-\text{NH}_2$). In an aqueous solution, the carboxyl group can lose a proton, and the amino group can accept a proton, resulting in a dipolar ion known as a zwitterion . Among the given options, only glycine is an amino acid and thus can form a zwitterion.