Final answer:
Serine and Threonine are the standard 20 amino acids that contain a chiral center in the side chain. Option c,d.
Step-by-step explanation:
The standard 20 amino acids consist of a central carbon atom called the α-carbon, which is bonded to a hydrogen atom, an amino group, a carboxyl group, and a side chain (R group).
Amino acids with a chiral center in their side chain are those in which the α-carbon is bound to four different groups. Based on this information, the amino acids that contain a chiral center in the side chain are c) Serine and d) Threonine. Glycine (a) and Alanine (b) do not have a chiral center in the side chain. Option c, d.