Which complex is likely to show optical activity :

Options

A. trans-`[Co(NH_(3))_(4)Cl_(2)]^(+)`
B. `[Cr(H_(2)O)_(6)]^(3+)`
C. cis-`[Co(NH_(3))_(2)(en)_(2)]`
D. trans-`[Co(NH_(3))_(2)(en)_(2)]^(3+)`

Answer

To determine which complex is likely to show optical activity, we need to analyze the given complexes based on their structures and the presence of symmetry elements. Optical activity arises when a compound has a non-superimposable mirror image, meaning it lacks a plane of symmetry.

### Step-by-Step Solution:

1. **Understanding Optical Activity**:
- Optical activity occurs in chiral molecules, which are non-superimposable on their mirror images. To determine if a complex is optically active, we need to check for symmetry.

2. **Analyzing the First Complex**:
- The first complex is [Co(NH3)2Cl2].
- In this case, the arrangement of ligands is trans, meaning the two NH3 ligands are opposite each other and the two Cl ligands are also opposite.
- When we draw the mirror image, it will be superimposable with the original structure.
- **Conclusion**: This complex is optically inactive.

3. **Analyzing the Second Complex**:
- The second complex is [Co(H2O)6] (octahedral with six identical ligands).
- Since all ligands are the same (H2O), any mirror image will also be superimposable with the original structure.
- **Conclusion**: This complex is also optically inactive.

4. **Analyzing the Third Complex (Cis Form)**:
- The third complex is [Co(NH3)2(en)] where en is ethylenediamine, and it is in a cis configuration.
- In this case, the NH3 ligands are adjacent to each other, and the en ligand is bidentate, creating a non-symmetric structure.
- When we draw the mirror image, it will not be superimposable with the original structure, indicating that this complex is chiral.
- **Conclusion**: This complex is optically active.

5. **Analyzing the Fourth Complex (Trans Form)**:
- The fourth complex is [Co(NH3)2(en)] in a trans configuration.
- Here, the NH3 ligands are opposite each other, similar to the first complex.
- The mirror image will be superimposable with the original structure.
- **Conclusion**: This complex is optically inactive.

6. **Final Conclusion**:
- After analyzing all the complexes, the one that shows optical activity is the cis form of [Co(NH3)2(en)].

### Answer:
The complex likely to show optical activity is the **cis form of [Co(NH3)2(en)]**.

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