Which of the following compound is optically inactive?

Options

A. `CH_(3)-CH_(2)-overset(OH)overset(|)(CH)-CH_(3)`
B.
C.
D.

Explanation

To determine which of the given compounds is optically inactive, we need to identify whether each compound has a stereogenic center (chiral carbon). A compound is optically inactive if it does not have any chiral centers.

### Step-by-Step Solution:

1. **Identify the Compounds**: We need to analyze each compound provided in the question to check for chiral centers.

2. **Analyze Compound A**:
- Compound A has four different groups attached to a carbon atom: ethyl, methyl, hydrogen, and hydroxyl (OH).
- Since all four groups are different, this carbon is a chiral center.
- **Conclusion**: Compound A is optically active.

3. **Analyze Compound B**:
- Compound B has one hydrogen, one A group, one A group, and one methyl (CS3).
- Here, two groups are identical (the two A groups), which means this carbon does not have four different groups.
- **Conclusion**: Compound B is not a chiral center and is optically inactive.

4. **Analyze Compound C**:
- Compound C has a carbon attached to hydrogen (H), chlorine (Cl), and two identical groups.
- Since there are two identical groups, this carbon is not a chiral center.
- **Conclusion**: Compound C is optically inactive.

5. **Analyze Compound D**:
- Compound D has one hydrogen, one methyl (CS3), and one A group.
- All three groups are different, making this carbon a chiral center.
- **Conclusion**: Compound D is optically active.

6. **Final Conclusion**:
- From the analysis, we find that Compound B and Compound C do not have chiral centers and are therefore optically inactive. However, since the question asks for one compound, we can conclude that **Compound B** is the one explicitly mentioned as optically inactive.

### Final Answer:
**Compound B is optically inactive.**