Which standard amino acid is optically inactive because its alpha carbon is not chiral?

### Why this is right Glycine’s side chain is hydrogen, so its alpha carbon has two identical hydrogen substituents. A carbon with two identical groups is not chiral and does not produce optical activity. ### The other options - **Tyrosine**: its alpha carbon has four different substituents and is chiral. - **Tryptophan**: its alpha carbon is chiral; its side chain contains an aromatic ring. - **Histidine**: its alpha carbon is chiral and its side chain contains an imidazole group. ### Terms - **Chiral**: having a structure that is not superimposable on its mirror image. - **Optical activity**: the ability of a substance to rotate plane-polarized light. ### Remember Glycine is the exception because its side chain is another hydrogen.