The crystal field theory assumes interaction between metal ion and the ligands as a purely electrostatic and ligands are supposed to be point charges.
Q. Amongst the following complexes which has square planar geometry?

Options

A. `[RhCl(CO)(P Ph_(3))_(2)]`
B. `K_(2)[Cu(SCN)_(4)]`
C. `K_(2)[Ni(PPH_(3))_(2)Cl_(2)]`
D. `MnO_(4)^(2-)`

Answer

To determine which of the following complexes has a square planar geometry, we will analyze the options provided based on the principles of crystal field theory and the characteristics of transition metals.

### Step-by-Step Solution:

1. **Understanding Square Planar Geometry**:
- Square planar geometry is typically observed in certain transition metal complexes, particularly those involving d8 metal ions. The geometry arises due to the specific arrangement of ligands around the central metal ion, which minimizes electron repulsion and stabilizes the complex.

2. **Identifying Transition Metals**:
- We need to identify the transition metals in the given complexes. Transition metals are typically found in groups 3 to 12 of the periodic table and have partially filled d-orbitals.

3. **Analyzing the Options**:
- Let's consider the common transition metals that can form square planar complexes:
- **Nickel (Ni)**, **Palladium (Pd)**, **Platinum (Pt)**, and **Rhodium (Rh)** are known to form square planar complexes, particularly in their +2 or +4 oxidation states.
- **Copper (Cu)** can also form square planar complexes, especially in the +2 oxidation state.

4. **Evaluating Each Complex**:
- For each complex, we need to check the oxidation state of the metal and its electron configuration:
- **Rhodium (Rh)**: In the +2 oxidation state, Rh has a d8 configuration, which is conducive to square planar geometry.
- **Copper (Cu)**: In the +2 oxidation state, Cu also has a d9 configuration, which can lead to square planar complexes but is less stable compared to d8.
- **Nickel (Ni)**: In the +2 oxidation state, Ni has a d8 configuration, which can also form square planar complexes.
- **Manganese (Mn)**: Typically does not form square planar complexes in its common oxidation states.

5. **Conclusion**:
- Among the options, **Rhodium (Rh)** is the most stable square planar complex due to its d8 configuration and its position in the second transition series, which allows for stronger ligand interactions and stabilization of the square planar geometry.

### Final Answer:
The complex that has square planar geometry is **Rhodium complex**.