Which of the following does not show optical isomerism?

Options

A. `[Co(en)_(3)]^(3+)`
B. trans `[CoCl_(2) (en)_(2)]^(+)`
C. `[Cr(ox)_(3)]^(+2)`
D. `cis[PtCl_(2) (en)_(2)]^(+2)`

Answer

To determine which of the given coordination compounds does not show optical isomerism, we need to analyze the symmetry properties of each compound. Optical isomerism occurs when a compound can exist in two non-superimposable mirror images, which typically happens in chiral molecules. A compound is considered achiral (and thus does not show optical isomerism) if it possesses a plane of symmetry.

### Step-by-Step Solution:

1. **Identify the Coordination Compounds**:
We need to examine the coordination compounds provided in the question. Let's assume we have four options, including bidentate ligands like ethylene diamine (en) and others.

2. **Determine Coordination Numbers**:
- For the first compound, which has ethylene diamine (en) as a bidentate ligand, the coordination number is 6, indicating an octahedral geometry.
- For the second compound, analyze if it has symmetrical ligands that can lead to a plane of symmetry.
- For the third compound, check if it has a similar structure to the first and if it can show optical isomerism.
- For the fourth compound, also check its structure and symmetry.

3. **Analyze Symmetry**:
- Draw the structures of the compounds.
- For the first compound (en), it is likely to be optically active due to lack of symmetry.
- For the second compound, if it has symmetrical ligands positioned opposite each other (trans configuration), it will have a plane of symmetry and thus be optically inactive.
- The third compound may also be optically active if it lacks symmetry.
- The fourth compound (cis configuration) may also lack symmetry, making it optically active.

4. **Conclusion**:
After analyzing the symmetry of each compound, we conclude that the second compound, which has a plane of symmetry due to its trans configuration, does not show optical isomerism. Therefore, it is the correct answer.

### Final Answer:
The compound that does not show optical isomerism is the second option (the one with a trans configuration).