Which of the following is not essential amino acid
Correct option is D. Glycine
$$\text{Essential amino acids cannot be made by the body so you must get them from your diet.}$$
The 9 essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
$$\text{Hence, glycine is not a essential amino acid}$$