Question

which option explains why this amino acid can act as both an acid and a base? amino acids

Explanation:

Amino - acids have an amino group ($-NH_2$) which can accept a proton (act as a base) and a carboxyl group ($-COOH$) which can donate a proton (act as an acid). This property makes them amphoteric.

Answer:

Amino - acids have both an amino group that can act as a base by accepting a proton and a carboxyl group that can act as an acid by donating a proton.