In Which case gemetrical isomer cis is possible with `M` as metal ion if complexes are square planar having `CN=4`?

Options

A. `a.MX_(2)Y_(2)`
B. `b.MX_(2)YZ`
C. `c.MXY_(2)Z`
D. `d.MX_(4)`

Answer

To determine in which cases geometrical isomerism (specifically cis isomerism) is possible for square planar complexes with a coordination number (CN) of 4, we will analyze the given options step by step.

### Step-by-Step Solution:

1. **Understanding Square Planar Geometry**:
- Square planar complexes have a central metal atom (M) surrounded by four ligands arranged in a square plane. This arrangement allows for the possibility of geometrical isomers (cis and trans) depending on the types of ligands attached.

2. **Analyzing the Ligand Combinations**:
- We will evaluate each option provided to see if it can form a cis isomer.

3. **Option A: M(X)2(Y)2**:
- Here, we have two identical ligands (X) and two identical ligands (Y).
- Arrangement: If we place X ligands adjacent to each other and Y ligands adjacent to each other, we can achieve a cis configuration.
- **Cis Isomer Possible**: Yes.

4. **Option B: M(X)2(Y)(Z)**:
- In this case, we have two identical ligands (X) and two different ligands (Y and Z).
- Arrangement: By placing the two X ligands next to each other and the Y and Z ligands on adjacent sides, we can achieve a cis configuration.
- **Cis Isomer Possible**: Yes.

5. **Option C: M(Y)2(Z)**:
- Here, we have two identical ligands (Y) and one different ligand (Z).
- Arrangement: Similar to the previous cases, placing the two Y ligands next to each other allows for a cis configuration.
- **Cis Isomer Possible**: Yes.

6. **Option D: M(X)4**:
- In this case, all four ligands are identical (X).
- Since all ligands are the same, there is no possibility of forming different arrangements that can lead to cis or trans isomers.
- **Cis Isomer Possible**: No.

### Conclusion:
The options that allow for the formation of cis isomers in square planar complexes with coordination number 4 are A, B, and C. Option D does not allow for any geometrical isomerism.

### Final Answer:
- **Cis isomerism is possible in cases A, B, and C.**
- **Cis isomerism is not possible in case D.**