Lactic acid (2-hydroxypropanoic acid) is an optically active compound. It can be made optically inactive by

Options

A. replacing its OH group by H
B. replacing its OH group by CI
C. replacing its OH group by Br
D. none of the above.

Explanation

To determine how lactic acid (2-hydroxypropanoic acid) can be made optically inactive, we need to analyze its structure and the concept of chirality.

### Step-by-Step Solution:

1. **Identify the Structure of Lactic Acid**:
- Lactic acid has the chemical formula C3H6O3. It consists of three carbon atoms, with a hydroxyl group (-OH) attached to the second carbon, making it a 2-hydroxypropanoic acid.
- The structural formula can be represented as:
```
CH3-CH(OH)-COOH
```
- The second carbon (C2) is a chiral center because it is attached to four different groups: a methyl group (CH3), a hydroxyl group (OH), a carboxylic acid group (COOH), and a hydrogen atom (H).

2. **Understanding Chirality and Optical Activity**:
- A compound is optically active if it has a chiral center, which allows it to rotate plane-polarized light. Lactic acid is optically active due to the presence of the chiral carbon (C2).

3. **Making Lactic Acid Optically Inactive**:
- To make lactic acid optically inactive, we need to remove the chirality. This can be achieved by replacing the hydroxyl group (-OH) with a hydrogen atom (H).
- If we replace the -OH group with H, the structure changes to:
```
CH3-CH2-COOH
```
- In this new structure, the second carbon (C2) now has two hydrogen atoms attached, which means it no longer has four different groups attached to it, thus losing its chirality.

4. **Evaluating the Options**:
- **Option A**: Replacing the -OH group with H → This makes the compound optically inactive (correct).
- **Option B**: Replacing the -OH group with Cl → This retains chirality as C2 still has four different groups.
- **Option C**: Replacing the -OH group with Br → This also retains chirality.
- **Option D**: None of the above → Incorrect since option A is valid.

5. **Conclusion**:
- The correct method to make lactic acid optically inactive is by replacing its hydroxyl group (-OH) with a hydrogen atom (H). Therefore, the answer is **Option A**.