In group separation, before precipitating out group III metal ions as hydroxides, it is necessary to boil the solution of the salt mixture with a few drops of concentrated `HNO_(3)` is treated. This is done to convert:

Options

A. `Co^(3+)` to `Co^(3+)`
B. `Fe^(2+)` to `Fe^(3+)`
C. `Mn^(3+)` to `MnO_(4)^(-)`
D. `Cr^(3+)` to `CrO_(4)^(2-)`

Answer

To answer the question regarding the necessity of boiling the solution of the salt mixture with concentrated HNO3 before precipitating out group III metal ions as hydroxides, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Group III Metal Ions**:
- Group III metal ions include Al³⁺, Fe³⁺, and Cr³⁺. These ions can form hydroxides which precipitate out of the solution.

2. **Role of Concentrated HNO3**:
- Concentrated nitric acid (HNO3) acts as an oxidizing agent. It has nitrogen in its highest oxidation state (+5), which allows it to oxidize certain ions in the solution.

3. **Boiling the Solution**:
- Boiling the solution with concentrated HNO3 helps in oxidizing certain metal ions. This is crucial because some metal ions exist in lower oxidation states and need to be converted to their higher oxidation states to form hydroxides.

4. **Identifying the Relevant Metal Ion**:
- Among the metal ions present, Fe²⁺ (ferrous ion) can be oxidized to Fe³⁺ (ferric ion) by concentrated HNO3. This conversion is necessary because only Fe³⁺ will precipitate as its hydroxide (Fe(OH)₃).

5. **Conclusion**:
- Therefore, the process of boiling the solution with concentrated HNO3 is specifically done to convert Fe²⁺ to Fe³⁺, allowing it to precipitate as Fe(OH)₃ when the solution is treated to form hydroxides.

### Final Answer:
In group separation, before precipitating out group III metal ions as hydroxides, it is necessary to boil the solution of the salt mixture with a few drops of concentrated HNO3 to convert Fe²⁺ to Fe³⁺.