Indicate the complex ion which shows geometrical isomerism.

Options

A. `[Cr(H_(2)O)_(4) Cl_(2)]^(+)`
B. `[Pt(NH_(3))_(3)Cl]`
C. `[Co(NH_(3))_(6)]^(3+)`
D. `[Co(CN)_(5) (NC)]^(3-)`

Explanation

To determine which complex ion shows geometrical isomerism, we need to analyze the ligands present in the complexes and their arrangements. Geometrical isomerism occurs when there are different spatial arrangements of ligands around a central metal atom in a coordination complex.

### Step-by-Step Solution:

1. **Identify the Complexes**: We need to look at the given options for complex ions and identify their structures. The complexes typically have the form MAxBy, where M is the metal, A represents one type of ligand, and B represents another type of ligand.

2. **Check for Different Ligands**: For geometrical isomerism to occur, there must be at least two different types of ligands in the complex. If all ligands are the same, no isomers can form.

3. **Analyze Each Complex**:
- **Option 1**: [Cr(NH3)6]³⁺ - This complex has only one type of ligand (NH3), so it cannot show geometrical isomerism.
- **Option 2**: [Co(CN)5(NC)] - This complex has five CN ligands and one NC ligand. Since there are not two different types of ligands in sufficient quantity to create isomers, it cannot show geometrical isomerism.
- **Option 3**: [Pt(NH3)3Cl] - This complex is square planar with three NH3 ligands and one Cl ligand. The presence of three identical ligands means it cannot show geometrical isomerism.
- **Option 4**: [Cr(H2O)4Cl2]⁺ - This complex has four H2O ligands and two Cl ligands. The presence of two different types of ligands allows for different spatial arrangements (cis and trans), which can lead to geometrical isomerism.

4. **Draw the Structures**: For the complex [Cr(H2O)4Cl2]⁺:
- **Cis Isomer**: The two Cl ligands are adjacent to each other.
- **Trans Isomer**: The two Cl ligands are opposite each other.

5. **Conclusion**: Among the given options, only [Cr(H2O)4Cl2]⁺ can show geometrical isomerism due to the presence of two different types of ligands in sufficient quantity.

### Final Answer:
The complex ion that shows geometrical isomerism is **[Cr(H2O)4Cl2]⁺**.