Which of the following has square planar structure

Options

A. `[NiCl_(4))]^(2-)`
B. `[Ni(CO)_(4)]`
C. `[Ni(CN)_(4)]^(2-)`
D. None of the above

Explanation

To determine which of the given compounds has a square planar structure, we need to analyze the oxidation states of the central metal ion (nickel in this case) and the nature of the ligands involved. The square planar geometry is typically associated with a coordination number of 4 and requires dsp² hybridization.

### Step-by-Step Solution:

1. **Identify the Central Metal and its Oxidation State**:
- The central metal in all compounds is nickel (Ni).
- Nickel has an atomic number of 28, with an electronic configuration of \( [Ar] 4s^2 3d^8 \).
- We need to determine the oxidation state of nickel in each compound to understand its electronic configuration in each case.

2. **Analyze the First Compound**:
- In the first compound, nickel is in the +2 oxidation state.
- The electronic configuration becomes \( 4s^0 3d^8 \).
- Chlorine is a weak field ligand, which means it does not cause pairing of electrons in the d-orbitals.
- Therefore, the hybridization is \( sp^3 \) (tetrahedral geometry), not square planar.

3. **Analyze the Second Compound**:
- In the second compound, nickel is in the 0 oxidation state.
- The electronic configuration remains \( 4s^2 3d^8 \).
- Carbon monoxide (CO) is a strong field ligand and can cause pairing of electrons.
- However, since we have \( 4s \) and \( 3d \) electrons available, the hybridization here is also \( sp^3 \) (tetrahedral geometry).

4. **Analyze the Third Compound**:
- In the third compound, nickel is again in the +2 oxidation state.
- The electronic configuration is \( 4s^0 3d^8 \).
- Cyanide (CN⁻) is a strong field ligand that causes pairing of electrons in the d-orbitals.
- The pairing of electrons allows for the utilization of the inner d-orbitals, leading to \( dsp^2 \) hybridization.
- This hybridization corresponds to a square planar geometry.

5. **Conclusion**:
- The only compound that exhibits a square planar structure is the one where nickel is in the +2 oxidation state with cyanide as the ligand. Therefore, the answer is **option C**.