Biology

The correct answer is B. Sulfur.

Explanation:

Sulfur is commonly found in the side chains of certain amino acids, particularly in cysteine and methionine. These amino acids contain sulfur atoms in their side chains, which play a crucial role in protein structure, such as forming disulfide bonds that help stabilize protein shapes.

Breakdown of other options:

A. Nitrogen

Nitrogen is a component of all amino acids, as part of the amine group (—NH₂) in every amino acid's structure.