Simplest amino acid which is optically inactive is

Options

A. Glycine
B. Proline
C. Leucine
D. Tryptophan

Answer

To determine the simplest amino acid that is optically inactive, we need to analyze the given options: glycine, proline, leucine, and tryptophan.

### Step-by-Step Solution:

1. **Understanding Amino Acids**: Amino acids are the building blocks of proteins. Each amino acid has a central carbon atom (alpha carbon) bonded to four different groups: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R group (side chain).

2. **Identifying Optical Activity**: An amino acid is optically active if it has a chiral (asymmetric) carbon atom, meaning the carbon is attached to four different groups. If an amino acid has no chiral carbon, it is optically inactive.

3. **Analyzing the Options**:
- **Glycine**: The R group is a hydrogen atom. Therefore, the alpha carbon is bonded to two hydrogen atoms and does not have four different groups. This means glycine does not have a chiral carbon and is optically inactive.
- **Proline**: This amino acid has a cyclic structure and contains a chiral carbon, making it optically active.
- **Leucine**: This amino acid has a chiral carbon and is also optically active.
- **Tryptophan**: This is an aromatic amino acid with a chiral carbon, thus it is optically active.

4. **Conclusion**: Since glycine is the only amino acid among the options that lacks a chiral carbon and is therefore optically inactive, it is the correct answer.

### Final Answer:
The simplest amino acid which is optically inactive is **glycine**.