Which would exhibit coordination isomerism
(a) `[Cr(NH_(3))_(6)][Co(CN)_(6)]`
(b) `[Cr(en)_(2)CI_(2)]^(o+)`
(c ) `[Cr(NH_(3))_(6)]CI_(3)`
(d) `[Cr(edta)]^(-)` .

Options

A. `[Cr(NH_(3))_(6)][Co(CN)_(6)]`
B. `[Cr(NH_(3))_(4)(CN)_(2)][Co(CN)_(4)(NH_(3))_(2)]`
C. `[Cr(NH_(3))_(3)(CN)_(3)][Co(NH_(3))_(3)(CN)_(3)]`
D. none of these

Answer

To determine which of the given compounds exhibits coordination isomerism, we first need to understand what coordination isomerism is. Coordination isomerism occurs when there are two or more coordination spheres that differ only by the arrangement of ligands around the central metal atom.

### Step-by-Step Solution:

1. **Identify Coordination Spheres**:
- Look at each compound and identify if there are multiple coordination spheres present.
- For example, in option (a) `[Cr(NH₃)₆][Co(CN)₆]`, we have two separate coordination complexes: one with Cr and another with Co.

2. **Analyze Each Option**:
- **(a) `[Cr(NH₃)₆][Co(CN)₆]`**: This compound has two distinct coordination spheres (one with Cr and one with Co), and they are linked by different ligands (NH₃ and CN). This can exhibit coordination isomerism.
- **(b) `[Cr(en)₂Cl₂]⁺`**: This has only one coordination sphere with a bidentate ligand (en) and two Cl ligands. There is no possibility for coordination isomerism here.
- **(c) `[Cr(NH₃)₆]Cl₃`**: This compound has only one coordination sphere with NH₃ ligands and does not allow for coordination isomerism.
- **(d) `[Cr(edta)]⁻`**: This is a hexa-dentate ligand that completely surrounds the chromium ion, thus it cannot exhibit coordination isomerism.

3. **Conclusion**:
- After analyzing all options, we find that only option (a) `[Cr(NH₃)₆][Co(CN)₆]` exhibits coordination isomerism due to the presence of two distinct coordination spheres with different ligands.

### Final Answer:
The compound that exhibits coordination isomerism is **(a) `[Cr(NH₃)₆][Co(CN)₆]`**.