Species which represent maximum crystal field stablisation energy :-

Options

A. `[Co(CN)_(6)]^(-3)`
B. `[Co(C_(2)O_(4))_(3)]^(-3)`
C. `[Ni(H_(2)O)_(6)]^(+2)`
D. Both (1) and (2)

Answer

To determine which species represents the maximum crystal field stabilization energy (CFSE), we need to consider two main factors: the charge on the metal ion and the strength of the ligands involved.

### Step-by-Step Solution:

1. **Understand Crystal Field Stabilization Energy (CFSE)**:
- CFSE is the energy stabilization that occurs when a transition metal ion is placed in a crystal field created by surrounding ligands. The strength of the ligands and the charge on the metal ion are critical in determining the CFSE.

2. **Identify the Metal Ion and Its Charge**:
- In the given question, we have cobalt in a +3 oxidation state for two of the compounds and nickel in a +2 oxidation state for another. The charge on the metal ion plays a significant role in the CFSE.

3. **Determine the Coordination Number**:
- All the complexes mentioned have a coordination number of 6. This means they are octahedral complexes, which is important for understanding how the ligands interact with the metal ion.

4. **Evaluate the Ligand Strength**:
- The ligands involved are:
- S2 (weakest ligand)
- Oxalate (C2O4^2−)
- Cyanide (CN^−, strongest ligand)
- The order of ligand strength is crucial because stronger ligands will lead to greater splitting of the d-orbitals, resulting in higher CFSE.

5. **Calculate CFSE for Each Complex**:
- For the cobalt complexes with +3 charge and coordination number of 6, we can conclude:
- The complex with CN^− will have the highest CFSE due to its strong field strength and the +3 charge on cobalt.
- The complex with oxalate will have a lower CFSE than the one with CN^−.
- The complex with S2 will have the lowest CFSE.

6. **Conclusion**:
- Among the given options, the complex with cobalt in the +3 oxidation state and coordinated with CN^− will exhibit the maximum crystal field stabilization energy due to the combination of a high charge and a strong ligand.

### Final Answer:
The species that represents maximum crystal field stabilization energy is the complex with cobalt in the +3 oxidation state coordinated with cyanide (CN^−).

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