The complex that can show optical isomerism is:

Options

A. `cis-[CrCl_(2)(o x)_(2)]^(-3)`
B. `trans -[CrCl_(2)(o x)_(2)]^(-3)`
C. Both (A) & (B)
D. Neither (A) and (B)

Explanation

To determine which complex can show optical isomerism, we need to understand the concept of optical isomerism and the types of complexes that can exhibit this property.

### Step-by-Step Solution:

1. **Understanding Optical Isomerism**:
- Optical isomerism occurs when two compounds have the same molecular formula and connectivity but differ in their spatial arrangement, making them non-superimposable mirror images (enantiomers).
- These isomers will rotate plane-polarized light in different directions.

2. **Identifying the Complexes**:
- The question mentions a specific complex: CrCl2OX^2-.
- Here, Cr is the central metal ion (Chromium), Cl are monodentate ligands, and OX is a bidentate ligand.

3. **Analyzing the Structure**:
- For the complex CrCl2OX^2-, we can visualize its cis and trans forms.
- The **cis form** has the bidentate ligand OX adjacent to each other, while the **trans form** has them opposite each other.

4. **Cis Form Analysis**:
- In the cis form, the arrangement of ligands creates a scenario where the complex can have non-superimposable mirror images.
- This non-superimposability indicates that the cis form can exhibit optical isomerism.

5. **Trans Form Analysis**:
- In the trans form, the arrangement of ligands allows for superimposable mirror images, meaning it does not exhibit optical isomerism.

6. **Conclusion**:
- Therefore, the complex CrCl2OX^2- in its cis form can show optical isomerism, while the trans form cannot.

### Final Answer:
The complex that can show optical isomerism is **CrCl2OX^2- (cis form)**.