Answer the question on basis of the passage given below:

In zwitter ionic form, amino acids show amphoteric behaviour as they react both with acids and bases.

Except glycine, all other naturally occurring \(\alpha \)- amino acids are optically active, since the \(\alpha \)-carbon atom is asymmetric. These exist both in 'D' and 'L' forms. Most naturally occurring amino acids have L-configuration. L-amino acids are represented by writing the \(NH_2\) group on the left hand side.

Optically inactive amino acid from the following is:

Glycine

The correct answer is option 2. Glycine.

The optically inactive amino acid from the options provided is 2. Glycine.

Optical Activity: For an amino acid (or any molecule) to be optically active, it must have a chiral center. A chiral center is typically a carbon atom that is attached to four different groups.

Glycine is the simplest amino acid with the structure \( NH_2-CH_2-COOH \). The central carbon atom (alpha carbon) in glycine is attached to two hydrogen atoms, an amino group (-NH₂), and a carboxyl group (-COOH). Since two of the groups attached to the alpha carbon are identical (both are hydrogen atoms), glycine does not have a chiral center and is therefore optically inactive.

Valine, Alanine, and Proline all have chiral centers because their alpha carbons are attached to four different groups. Hence, they are optically active.

Thus, Glycine is the correct answer because it is optically inactive.