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 will analyze the given options based on the criteria for geometrical isomerism.

### Step-by-Step Solution:

1. **Understanding Geometrical Isomerism**:
Geometrical isomerism occurs in coordination compounds when ligands can be arranged in different spatial configurations around the central metal atom. This typically happens when there are two or more different types of ligands present.

2. **Analyzing Option A**:
The complex is [Cr(H2O)4Cl2].
- Here, chromium (Cr) is the central metal atom (M).
- There are 4 water (H2O) ligands (denoted as A) and 2 chloride (Cl) ligands (denoted as B).
- The formula can be written as MA4B2.
- Since there are two types of ligands (A and B), geometrical isomerism is possible.

3. **Drawing Combinations for Option A**:
- Possible arrangements can be AAABBB (where A = H2O and B = Cl).
- The different arrangements can be:
- AABB (cis form)
- ABAB (trans form)
- Since these arrangements are different, geometrical isomerism is possible in this complex.

4. **Analyzing Option B**:
The complex is [Pt(NH3)3Cl].
- Here, platinum (Pt) is the central metal atom.
- There are 3 ammonia (NH3) ligands (A) and 1 chloride (Cl) ligand (B).
- The formula can be written as MA3B.
- Since there is only one type of B ligand, geometrical isomerism is not possible.

5. **Analyzing Option C**:
The complex is [Co(NH3)6]3+.
- Here, cobalt (Co) is the central metal atom.
- All 6 ligands are ammonia (NH3), so there is no variation in ligand type.
- The formula is MA6.
- Since all ligands are the same, geometrical isomerism is not possible.

6. **Analyzing Option D**:
The complex is [Co(CN)5NC].
- Here, cobalt (Co) is the central metal atom.
- There are 5 cyanide (CN) ligands (A) and 1 isocyanide (NC) ligand (B).
- The formula can be written as MA5B.
- Since there is only one type of B ligand, geometrical isomerism is not possible.

7. **Conclusion**:
After analyzing all options, only option A ([Cr(H2O)4Cl2]) shows geometrical isomerism due to the presence of two different types of ligands.

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