Which of the following will show optical activity?

Options

A. `Cis-[Co(NH_(3))_(2)(en)_(2)]^(3+)`
B. `Trans-[Co(NH_(3))_(2)(en)_(2)]^(3+)`
C. `[Co(NH_(3))_(6)]^(3+)`
D. `Trans-[Co(H_(2)O)_(4)CI_(2)]^(+)`

Answer

To determine which of the given coordination compounds will show optical activity, we need to analyze their structures and symmetry. Optical activity occurs when a compound has non-superimposable mirror images, meaning it does not possess a plane of symmetry.

### Step-by-Step Solution:

1. **Identify the Ligands and Coordination Number**:
- The question involves coordination compounds with different ligands. We need to identify whether the ligands are monodentate or bidentate.
- Monodentate ligands bind through a single donor atom, while bidentate ligands can bind through two donor atoms.

2. **Draw the Structures**:
- For the complex with a monodentate ligand (like amine) and a bidentate ligand (like ethylene diamine), we can visualize the structure in an octahedral geometry.
- Place the central metal ion (e.g., cobalt) at the center and arrange the ligands accordingly. In the cis configuration, the monodentate ligands will be adjacent to each other.

3. **Check for Optical Isomers**:
- Draw the mirror image of the structure. If the mirror image cannot be superimposed on the original structure, it indicates the presence of optical isomers.
- For the cis configuration with one monodentate ligand and one bidentate ligand, the mirror images will not be superimposable, indicating optical activity.

4. **Analyze Other Configurations**:
- For the trans configuration with only monodentate ligands, the structure will have a plane of symmetry. The mirror image will be superimposable, indicating that it is optically inactive.
- Similarly, if a complex contains only one type of ligand, it will also lack optical isomers due to symmetry.

5. **Conclusion**:
- After analyzing the structures and their mirror images, we conclude that the complex with the cis configuration of a monodentate and a bidentate ligand shows optical activity, while the others do not.

### Final Answer:
The correct option that shows optical activity is **Option A**.