Which one of the following is expected to exhibit optical isomerism (en=ethylenediamine)?

Options

A. `Cis-[Pt(NH_(3))_(2)Cl_(2)]`
B. `Trans-[Co(en)_(2)Cl_(2)]^(+)`
C. `Trans-[Pt(NH_(3))_(2)Cl_(2)]`
D. `Cis-[Co(en)_(2)Cl_(2)]^(+)`

Explanation

To determine which of the given compounds exhibits optical isomerism, we need to analyze the structures of each compound and check for the presence of chiral centers. A compound exhibits optical isomerism if it has non-superimposable mirror images, known as enantiomers.

### Step-by-Step Solution:

1. **Understand Optical Isomerism**:
Optical isomerism occurs when a compound can exist in two forms that are mirror images of each other but cannot be superimposed. These forms are called enantiomers.

2. **Identify the Compounds**:
We need to analyze the four options provided. The central metal ion in each compound will be surrounded by ligands, and we need to determine their spatial arrangement.

3. **Analyze Option A**:
- The structure involves a metal (let's say Pt) with ligands arranged in a certain way.
- After drawing the structure and its mirror image, we find that the two images can be superimposed.
- **Conclusion**: This compound does not exhibit optical isomerism.

4. **Analyze Option B**:
- This compound has a cobalt center with ligands arranged in a trans configuration.
- Drawing the structure and its mirror image shows that they can be superimposed.
- **Conclusion**: This compound does not exhibit optical isomerism.

5. **Analyze Option C**:
- Similar to Option B, this compound has a trans configuration.
- Again, upon drawing the structure and its mirror image, we find that they can be superimposed.
- **Conclusion**: This compound does not exhibit optical isomerism.

6. **Analyze Option D**:
- This compound has a cis configuration with one chlorine atom above the plane and another in the plane, while the ethylenediamine ligands are positioned differently.
- Upon drawing the structure and its mirror image, we find that the two images cannot be superimposed.
- **Conclusion**: This compound exhibits optical isomerism.

7. **Final Answer**:
- The compound that exhibits optical isomerism is **Option D: cis-[Co(en)₂Cl₂]**.