Which of the following is more stable ?
(1) `K_(4)[Fe(CN)_(6)] or K_(3)[Fe(CN)_(6)]`
(2) `[Co(NH_(3))_(6)]^(3+) or [Co(en)_(2)(NH_(3))_(2)]^(3+)`
(3) `[NiCl_(4)]^(2-) or [Ni(CN)_(4)]^(2-)`

Explanation

To determine the stability of the given coordination compounds, we will analyze each pair based on the charge on the central metal ion and the nature of the ligands.

### Step 1: Analyze K₄[Fe(CN)₆] vs K₃[Fe(CN)₆]

1. **Determine the oxidation state of Fe in both complexes.**
- For K₄[Fe(CN)₆]: The overall charge of the complex is -4 (from K⁴). Since CN is a neutral ligand, we can set up the equation:
\[
x + 6(-1) = -4 \implies x - 6 = -4 \implies x = +2
...