Colour of ferrous sulphate crystals

Options

A. orange
B. green
C. blue
D. yellow

Explanation

### Step-by-Step Solution

1. **Identify the Compound**: The question asks about the color of ferrous sulfate crystals, which is represented by the chemical formula FeSO₄.

2. **Understand the Hydrate Form**: Ferrous sulfate commonly exists in a hydrated form, specifically as ferrous sulfate heptahydrate (FeSO₄·7H₂O). This means that for every formula unit of ferrous sulfate, there are seven water molecules associated with it.

3. **Determine the Color of Anhydrous Ferrous Sulfate**: The anhydrous form of ferrous sulfate (FeSO₄) is typically pale green in color. This is due to the presence of unpaired electrons in the iron (Fe²⁺) ions, which can absorb certain wavelengths of light and thus exhibit color.

4. **Effect of Hydration on Color**: When ferrous sulfate crystallizes with water (as in the heptahydrate form), the color can change. However, the heptahydrate form still retains a greenish hue but may appear lighter or more vivid due to the interaction with water molecules.

5. **Conclusion**: The color of ferrous sulfate crystals, particularly in its common hydrated form (FeSO₄·7H₂O), is generally described as green.

### Final Answer
The color of ferrous sulfate crystals is **green**.

---