Name the chief ores of tin, iron and aluminium. What methods are employed for the concentration or purification of their ores ?

Explanation

### Step-by-Step Solution

1. **Identify the Chief Ores:**
- **Tin:** The chief ore of tin is **Cassiterite** (SnO2).
- **Iron:** The chief ore of iron is **Hematite** (Fe2O3).
- **Aluminium:** The chief ore of aluminium is **Bauxite** (Al2O3·2H2O).

2. **Methods of Concentration or Purification:**
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