Why is it essential to oxidise ferrous salt to ferric salt in group III?

Explanation

### Step-by-Step Solution:

1. **Understanding Group III Precipitation**: In qualitative inorganic analysis, Group III cations include iron (Fe), aluminum (Al), and chromium (Cr). When analyzing these cations, it is crucial to ensure that they are in the correct oxidation state for effective precipitation.

2. **Ferrous vs. Ferric Salts**: Ferrous salts contain iron in the +2 oxidation state (Fe²⁺), while ferric salts contain iron in the +3 oxidation state (Fe³⁺). The oxidation state of iron affects its solubility and precipitation behavior.

3. **Role of Ammonium Chloride (NH₄Cl)**: When ammonium chloride is added to a solution containing ferrous ions, it does not facilitate the complete precipitation of ferrous hydroxide (Fe(OH)₂). This is because Fe²⁺ ions can remain soluble in the presence of NH₄Cl.

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