The number of water of crystallization in green vitriol is…..

Explanation

To determine the number of water of crystallization in green vitriol, we follow these steps:

### Step-by-Step Solution:

1. **Identify the Chemical Name**:
Green vitriol is commonly known as iron(II) sulfate.

2. **Recognize the Hydrate Form**:
The specific form of iron(II) sulfate we are discussing is the heptahydrate, which means it contains water molecules in its crystalline structure.

3. **Write the Chemical Formula**:
The chemical formula for green vitriol is FeSO4·7H2O. In this formula, Fe represents iron, SO4 represents the sulfate ion, and 7H2O indicates that there are 7 water molecules associated with each formula unit of iron(II) sulfate.

4. **Count the Water Molecules**:
From the formula FeSO4·7H2O, we can see that there are 7 water molecules (H2O) present.

5. **Conclusion**:
Therefore, the number of water of crystallization in green vitriol is 7.

### Final Answer:
The number of water of crystallization in green vitriol is **7**.

---