The most stable ion is:

Options

A. `[Fe(C_(2)O_(4))_(3)]^(3-)`
B. `[Fe(CN)_(6)]^(3-)`
C. `[Fe(CN)_(6)]^(4-)`
D. `[Fe(H_(2)O)_(6)]^(3+)`

Answer

To determine the most stable ion among the given options, we will analyze the stability based on the ligand strength, oxidation state of the central metal ion, and the nature of the metal ion. Let's break down the solution step by step.

### Step-by-Step Solution:

1. **Identify the Ligands and Their Strengths**:
- The ligands mentioned are oxalate (C2O4), cyano (CN), and aqua (H2O).
- According to the spectrochemical series, the strength of ligands can be ranked as follows:
- Strong field ligands: Cyano (CN)
- Weak field ligands: Oxalate (C2O4) and Aqua (H2O)

2. **Determine the Oxidation States of the Metal Ion**:
- For the complex [Fe(CN)6]³⁻:
- Let the oxidation state of Fe be x.
- The charge of cyano (CN) is -1, and there are 6 cyano ligands.
- The equation becomes: x + (6 * -1) = -3
- Solving for x gives: x - 6 = -3 → x = +3
- For the complex [Fe(CN)6]²⁻:
- Similarly, let the oxidation state of Fe be x.
- The equation becomes: x + (6 * -1) = -2
- Solving for x gives: x - 6 = -2 → x = +4

3. **Compare the Oxidation States**:
- The oxidation states calculated are +3 for [Fe(CN)6]³⁻ and +2 for [Fe(CN)6]²⁻.
- Higher oxidation states generally lead to greater stability in coordination complexes, especially with strong field ligands.

4. **Conclusion**:
- Since [Fe(CN)6]³⁻ has a higher oxidation state (+3) and is coordinated with a strong field ligand (CN), it will be more stable than [Fe(CN)6]²⁻ which has a lower oxidation state (+2).
- Therefore, the most stable ion is [Fe(CN)6]³⁻.

### Final Answer:
The most stable ion is [Fe(CN)6]³⁻.