Which one of the following statements is correct?

Options

A. All amino acids are optically active
B. All amino acids except glycine are optically active
C. All amino acids except glutamic acid are optically active
D. All amino acids except lysine are optically active

Explanation

To determine which statement about amino acids is correct, we will analyze each option based on the optical activity of amino acids, particularly focusing on glycine and glutamic acid.

### Step-by-Step Solution:

1. **Understanding Optical Activity**:
- Optical activity refers to the ability of a compound to rotate plane-polarized light. A molecule is optically active if it has a chiral center, which means it has four different groups attached to a carbon atom.

2. **Analyzing Glycine**:
- Glycine is the simplest amino acid with the structure:
- NH2 (amino group)
- COOH (carboxyl group)
- H (hydrogen)
- H (another hydrogen)
- The central carbon in glycine is attached to two hydrogen atoms, making it symmetrical. Therefore, glycine is **optically inactive**.

3. **Analyzing Glutamic Acid**:
- Glutamic acid has the structure:
- NH2 (amino group)
- COOH (carboxyl group)
- CH2 (methylene group)
- CH2 (another methylene group)
- The central carbon in glutamic acid is attached to four different groups (NH2, COOH, CH2, and H), making it a chiral center. Therefore, glutamic acid is **optically active**.

4. **Evaluating the Options**:
- **Option 1**: "All amino acids are optically active."
- This is **incorrect** because glycine is optically inactive.
- **Option 2**: "All amino acids except glycine are optically active."
- This is **correct** because all other amino acids, including glutamic acid, are optically active.
- **Option 3**: "All amino acids except glutamic acid are optically active."
- This is **incorrect** because glutamic acid itself is optically active.
- **Option 4**: "All amino acids except glycine are optically active."
- This is a repeat of Option 2 and is **correct**.

5. **Conclusion**:
- The correct statement is **Option 2**: "All amino acids except glycine are optically active."