State the number of water molecules present in crystal of washing soda and plaster of paris. What are these water molecules called as?

Explanation

**Step-by-Step Solution:**

1. **Identify Washing Soda:**
- Washing soda is chemically known as sodium carbonate.
- The formula for washing soda is Na2CO3·10H2O.

2. **Determine the Number of Water Molecules in Washing Soda:**
- From the formula, we can see that there are 10 water molecules associated with each formula unit of washing soda.
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