Which one of the following statements is correct

Options

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

Explanation

To determine which statement about amino acids is correct, we need to analyze the properties of amino acids, particularly their optical activity.

### Step-by-Step Solution:

1. **Understanding Optical Activity**:
- Optical activity refers to the ability of a compound to rotate plane-polarized light. This property is typically exhibited by chiral molecules, which have a carbon atom bonded to four different groups (chiral center).

2. **Identifying Amino Acids**:
- Amino acids are organic compounds that serve as the building blocks of proteins. The general structure of an amino acid can be represented as NH2-CHR-COOH, where R represents the side chain that varies among different amino acids.

3. **Analyzing Glycine**:
- Glycine is the simplest amino acid, where R is a hydrogen atom (H). Its structure is NH2-CH2-COOH. Since the central carbon (C) in glycine is bonded to two hydrogen atoms (H), it does not have four different substituents. Therefore, glycine is not chiral and is optically inactive.

4. **Evaluating Other Amino Acids**:
- All other standard amino acids (except glycine) have a chiral center, meaning they have four different groups attached to their central carbon. This makes them optically active.

5. **Reviewing the Statements**:
- **Statement 1**: "All amino acids except lysine are optically active." - Incorrect, as glycine is also optically inactive.
- **Statement 2**: "All amino acids are optically active." - Incorrect, as glycine is optically inactive.
- **Statement 3**: "All amino acids except glycine are optically active." - Correct, as all other amino acids have a chiral center.
- **Statement 4**: "All amino acids except glutamic acids are optically active." - Incorrect, as glycine is also optically inactive.

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

### Final Answer:
The correct statement is: **"All amino acids except glycine are optically active."**