In the commercial extraction of iron, roasting is adopted because

Options

A. It removes impurities of `S, As` and `Sb` in the form of their elemental vapour
B. It prevents slag formation by `Fe_(2)O_(3)`
C. It prevents slag formation by `FeO`
D. Limonite is converted into its anhydrous form

Answer

### Step-by-Step Solution:

1. **Understanding Roasting**: Roasting is a metallurgical process where the ore is heated in the presence of oxygen. This process converts the ore into its oxide form without reaching the melting point.

2. **Conversion of Iron Oxides**: In the extraction of iron, the iron ore (like FeO) is converted to iron(III) oxide (Fe2O3) through roasting. This conversion is essential because Fe2O3 does not react with silica (SiO2) to form slag, unlike FeO.

3. **Slag Formation**: When FeO is present, it reacts with SiO2 to form slag (FeSiO3). By converting FeO to Fe2O3 through roasting, the formation of slag is prevented, which simplifies the extraction process.

4. **Removal of Impurities**: During roasting, impurities such as sulfur (S), arsenic (As), and antimony (Sb) are oxidized to their volatile oxides (e.g., SO2, As2O3, Sb2O3). These volatile oxides can be easily removed from the system due to their gaseous nature.

5. **Anhydrous Limonite**: Roasting also helps in converting limonite (Fe2O3·3H2O) into its anhydrous form by removing the water molecules. This conversion is beneficial for the extraction process.

6. **Conclusion**: The main reasons for adopting roasting in the commercial extraction of iron are:
- Conversion of FeO to Fe2O3, which prevents slag formation.
- Removal of volatile impurities in the form of oxides.
- Conversion of hydrated limonite to anhydrous limonite.

### Final Answer:
Roasting is adopted in the commercial extraction of iron because it converts FeO to Fe2O3, preventing slag formation, and allows for the removal of volatile impurities.

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