Among the following, the most stable complex is
(i). `[Fe(H_2O)_6]^(3+)`
(ii). `[Fe(NH_3)_6]^(3+)`
(iii). `[Fe(C_2O_4)_3]^(3-)`
(iv). `[FeCl_6]^(3-)`

Explanation

To determine which of the given complexes is the most stable, we will analyze each complex based on the types of ligands and their coordination properties.

### Step-by-Step Solution:

1. **Identify the oxidation state of Iron in each complex:**
- For `[Fe(H2O)6]^(3+)`: Iron is in +3 oxidation state.
- For `[Fe(NH3)6]^(3+)`: Iron is also in +3 oxidation state.
- For `[Fe(C2O4)3]^(3-)`: Iron is in +3 oxidation state.
...