Which one of the following statements is correct ?

Options

A. (a) All amino acids except lysine are optically active
B. (b) All amino acids are optically active
C. (c) All amino acids except glycine are optically active
D. (d) All amino acids except glutamic acid are optically active

Answer

To determine which statement regarding amino acids is correct, we need to analyze the properties of amino acids, particularly focusing on their optical activity. Here's a step-by-step solution:

### Step 1: Understand the Structure of Amino Acids
Amino acids have a general structure that includes:
- An amino group (-NH2)
- A carboxylic acid group (-COOH)
- A hydrogen atom
- A variable R group (side chain)

The central carbon atom (alpha carbon) is attached to these four different groups.

### Step 2: Identify Optical Activity
A compound is optically active if it has a chiral center, which means it must have four different groups attached to a carbon atom. If two of the groups are the same, the compound is achiral and optically inactive.

### Step 3: Analyze Each Statement
1. **Statement A**: "All amino acids except glycine are optically active."
2. **Statement B**: "All amino acids are optically active."
3. **Statement C**: "All amino acids except glycine are optically active."
4. **Statement D**: "All amino acids except glutamic acid are optically active."

### Step 4: Evaluate Each Statement
- **Glycine**: The R group in glycine is a hydrogen atom (H), making it have two identical groups attached to the alpha carbon (NH2 and H). Therefore, glycine is **not optically active**.

- **Other Amino Acids**: Most amino acids have four different groups attached to their alpha carbon, making them optically active.

- **Statement A**: This is incorrect because it implies that glycine is the only exception, but it does not specify that glycine itself is optically inactive.

- **Statement B**: This is incorrect because glycine is not optically active.

- **Statement C**: This is correct. All amino acids except glycine are optically active.

- **Statement D**: This is incorrect because glutamic acid is optically active.

### Conclusion
The correct statement is **Statement C**: "All amino acids except glycine are optically active."