Which of the following complex is most stable ?

Options

A. `[Co(H_(2)O)_(6)]Cl_(3)`
B. `K_(3)[Co(CN)_(6)`
C. `K_(3)[Co(O X)_(3)]`
D. `K_(3)[CoF_(6)]`

Answer

To determine which complex is the most stable among the given options, we need to analyze the ligands involved in each complex and their relative strengths according to the spectrochemical series.

### Step-by-Step Solution:

1. **Identify the Ligands**:
- Look at the ligands present in each complex. Common ligands might include water (H2O), fluoride (F-), and oxalate (C2O4^2-), among others.

2. **Determine Ligand Strength**:
- Refer to the spectrochemical series, which ranks ligands based on their field strength. Strong field ligands stabilize the complex more than weak field ligands.
- In general, ligands like CN- (cyanide) are considered strong field ligands, while H2O and F- are weak field ligands.

3. **Compare the Ligands**:
- If the complex contains weak field ligands (like H2O or F-), it will be less stable compared to complexes with strong field ligands (like CN- or oxalate).
- Bidentate ligands (like oxalate) can provide additional stability due to the chelate effect, but they are not always stronger than monodentate ligands like CN-.

4. **Analyze the Given Options**:
- For example, if one complex is [Cu(H2O)6]²⁺ and another is [Cu(CN)4]²⁻, the latter will be more stable due to the presence of the strong field ligand CN-.
- If comparing [Cu(C2O4)]²⁻ and [Cu(CN)4]²⁻, the CN- complex will still be more stable due to the strength of the ligand.

5. **Conclusion**:
- Based on the analysis, the complex with the strongest ligand (in this case, CN-) will be the most stable.
- Therefore, the answer is the complex that contains CN- as a ligand, which is option 2.

### Final Answer:
The most stable complex is the one containing CN- as a ligand, which is option 2.