Which of the following molecules has a meso stereoisomer?

Options

A. `CH_(3)-overset(Cl) overset(|)(CH)-CH_(2)-overset(Br) overset(|)(CH)-CH_(3)`
B. trans-2-hexene
C. `CH_(3)-underset(Cl) underset(|)(CH)-CH_(2)-CH_(2)-CH_(2)-Cl`
D. `CH_(3)CH_(2) underset(Cl) underset(|)(CH)- underset(Cl) underset(|)(CH)-CH_(2)CH_(3)`

Answer

To determine which of the given molecules has a meso stereoisomer, we first need to understand what a meso compound is. A meso compound is a molecule that has multiple stereogenic centers but is not optically active due to an internal plane of symmetry. This means that even though it has chiral centers, the overall molecule is achiral.

### Step-by-Step Solution:

1. **Identify the Stereogenic Centers**:
- For each molecule, identify the carbon atoms that have four different substituents attached to them. These are the stereogenic centers.

2. **Check for Symmetry**:
- Look for an internal plane of symmetry in the molecule. If the molecule can be divided into two symmetrical halves, it may be a meso compound.

3. **Analyze Each Option**:
- **Option 1**: CH3-CHCl-CH2-CHBr-CH3
- This molecule has stereogenic centers but does not have an internal plane of symmetry. Therefore, it is not a meso compound.
- **Option 2**: trans-2-hexene
- This molecule is not a meso compound as it does not have the required symmetry.
- **Option 3**: CH3-CHCl-CH2-CH2-CH2Cl
- This molecule has stereogenic centers but lacks an internal plane of symmetry, so it is not a meso compound.
- **Option 4**: CH3-CH2-CHCl-CHCl-CH2-CH3
- This molecule has two stereogenic centers and possesses an internal plane of symmetry, making it a meso compound.

4. **Conclusion**:
- The only molecule that qualifies as having a meso stereoisomer is **Option 4**: CH3-CH2-CHCl-CHCl-CH2-CH3.

### Final Answer:
The molecule that has a meso stereoisomer is **Option 4: CH3-CH2-CHCl-CHCl-CH2-CH3**.