Identifying a Polar Uncharged Amino Acid

Amino acids are the building blocks of proteins, each consisting of a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a variable R group that determines the characteristics of the amino acid. There are 20 different amino acids that are used to synthesize proteins in living organisms. When amino acids are linked together by peptide bonds, they form polypeptides, which fold into functional proteins.

Which of the following amino acids is classified as a polar, uncharged amino acid?