A student strongly heats hydrated ferrous sulphate salt in a dry test-tube. He would observe a :

Options

A. yellow residue
B. brown residue
C. light green residue
D. white residue

Explanation

### Step-by-Step Solution:

1. **Understanding Hydrated Ferrous Sulphate**:
- Hydrated ferrous sulphate is a compound that contains water molecules in its structure. Its chemical formula is typically represented as FeSO₄·7H₂O, which indicates that it has seven water molecules associated with each ferrous sulphate unit.

2. **Heating the Hydrated Ferrous Sulphate**:
- When hydrated ferrous sulphate is strongly heated in a dry test tube, the heat causes the water molecules to evaporate. This process is known as dehydration.

3. **Formation of Anhydrous Ferrous Sulphate**:
- As the water is lost, the hydrated ferrous sulphate transforms into anhydrous ferrous sulphate (FeSO₄). This compound does not contain any water molecules.

4. **Decomposition of Anhydrous Ferrous Sulphate**:
- Upon continued heating, the anhydrous ferrous sulphate further decomposes. The decomposition reaction produces ferric oxide (Fe₂O₃), sulfur dioxide (SO₂), and sulfur trioxide (SO₃) gases.

5. **Observation of Residue**:
- The solid residue left after the decomposition is ferric oxide, which is known to have a reddish-brown color.

6. **Conclusion**:
- Therefore, the student would observe a reddish-brown residue after strongly heating hydrated ferrous sulphate in a dry test tube.

### Final Answer:
The student would observe a **reddish-brown residue** after heating hydrated ferrous sulphate.

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