Which amino acid is not optically active?

• A. Glycine
• B. Leucine
• C. Isoleucine
• D. Valine

The amino acid that is not optically active is Glycine. This is because glycine is the only amino acid that does not have a chiral center, meaning it does not have four different groups attached to its central carbon atom.

Understanding Optical Activity

Optical activity refers to the ability of a compound to rotate plane-polarized light. Most amino acids are optically active due to their chiral centers, which allow them to exist in two mirror-image forms (enantiomers).

Characteristics of Amino Acids

• Glycine: No chiral center, thus not optically active.
• Leucine: Has a chiral center, optically active.
• Isoleucine: Has a chiral center, optically active.
• Valine: Has a chiral center, optically active.

In summary, glycine stands out as the only amino acid that lacks optical activity due to its unique structure.