Which one of the following is not an essential amino acid?

Alanine

The answer is (4) alanine.

Essential amino acids are amino acids that cannot be synthesized by the human body and must be obtained from the diet. Alanine is not an essential amino acid because it can be synthesized by the human body.

The other three amino acids, valine, leucine, and lysine, are essential amino acids. They must be obtained from the diet in order for the body to function properly.

Here is a table that summarizes the essential amino acids: