Which of the following is a diamagnetic complex

Options

A. `[Co(NH_(3))_(6)]^(3+)`
B. `[NiCl_(4)]^(2-)`
C. `[CuCl_(4)]^(2-)`
D. `[Fe(H_(2)O)_(6)]^(3+)`

Explanation

To determine which of the given complexes is diamagnetic, we need to analyze the electron configurations of each complex and the nature of their ligands. A diamagnetic complex is one that has all its electrons paired, while a paramagnetic complex has unpaired electrons.

### Step-by-Step Solution:

1. **Identify the Complexes**: The question provides several complexes. We will analyze each one to find the diamagnetic complex.

2. **Analyze the First Complex: [Co(NH3)6]³⁺**:
- **Ligand**: Ammonia (NH3) is a neutral ligand and a strong field ligand.
- **Oxidation State of Cobalt**: In this complex, cobalt is in the +3 oxidation state.
- **Electron Configuration**: The electron configuration of Co³⁺ is [Ar] 3d⁶.
- **Electron Pairing**: As NH3 is a strong field ligand, it causes pairing of electrons. Therefore, all 6 electrons will be paired.
- **Conclusion**: This complex is diamagnetic as there are no unpaired electrons.

3. **Analyze the Second Complex: [NiCl4]²⁻**:
- **Ligand**: Chloride (Cl⁻) is a weak field ligand.
- **Oxidation State of Nickel**: Nickel is in the +2 oxidation state.
- **Electron Configuration**: The electron configuration of Ni²⁺ is [Ar] 3d⁸.
- **Electron Pairing**: Since Cl⁻ is a weak field ligand, there will be no pairing of electrons, resulting in unpaired electrons.
- **Conclusion**: This complex is paramagnetic.

4. **Analyze the Third Complex: [CuCl4]²⁻**:
- **Ligand**: Chloride (Cl⁻) is again a weak field ligand.
- **Oxidation State of Copper**: Copper is in the +2 oxidation state.
- **Electron Configuration**: The electron configuration of Cu²⁺ is [Ar] 3d⁹.
- **Electron Pairing**: As Cl⁻ is a weak field ligand, there will be no pairing, leading to unpaired electrons.
- **Conclusion**: This complex is paramagnetic.

5. **Analyze the Fourth Complex: [Fe(H2O)6]³⁺**:
- **Ligand**: Water (H2O) is a neutral ligand and a weak field ligand.
- **Oxidation State of Iron**: Iron is in the +3 oxidation state.
- **Electron Configuration**: The electron configuration of Fe³⁺ is [Ar] 3d⁵.
- **Electron Pairing**: As H2O is a weak field ligand, there will be no pairing of electrons, resulting in unpaired electrons.
- **Conclusion**: This complex is paramagnetic.

### Final Conclusion:
Among the complexes analyzed, the first complex, [Co(NH3)6]³⁺, is the only diamagnetic complex.