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 following coordination compounds does not show optical isomerism, we will analyze each option based on the concept of superimposable mirror images.

### Step-by-Step Solution:

1. **Understanding 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 known as enantiomers.

2. **Identifying the Given Complexes:**
- We need to analyze the following complexes:
- A: [Co(en)3]^(3+)
- B: [CoCl2(en)2]^(+)
- C: [Cr(ox)3]^(3-)
- D: [PtCl2(en)2]

3. **Analyzing Each Complex:**
- **Complex A: [Co(en)3]^(3+)**
- This complex has an octahedral geometry with three bidentate ethylenediamine (en) ligands.
- The mirror images of this complex are not superimposable, indicating that it shows optical isomerism.

- **Complex B: [CoCl2(en)2]^(+)**
- This complex has a trans configuration where the two chloride ligands are opposite each other.
- The mirror images of this complex can be superimposed, indicating that it does not show optical isomerism.

- **Complex C: [Cr(ox)3]^(3-)**
- This complex also has an octahedral geometry with three bidentate oxalate (ox) ligands.
- The mirror images are not superimposable, indicating that it shows optical isomerism.

- **Complex D: [PtCl2(en)2]**
- This complex has a cis configuration with two bidentate ethylenediamine ligands and two chloride ligands.
- The mirror images are not superimposable, indicating that it shows optical isomerism.

4. **Conclusion:**
- Among the given complexes, only **Complex B: [CoCl2(en)2]^(+)** does not show optical isomerism because its mirror images are superimposable.

### Final Answer:
**Option B: [CoCl2(en)2]^(+) does not show optical isomerism.**