Washing soda has the formula:

Options

A. `Na_(2)CO_(3)`
B. `Na_(2)CO_(3).H_(2)O`
C. `Na_(2)CO_(3).7H_(2)O`
D. `Na_(2)CO_(3).10H_(2)O`

Explanation

**Step-by-Step Solution:**

1. **Understanding the term "Washing Soda":**
- Washing soda is commonly known as sodium carbonate, which is used in various cleaning and industrial applications.

2. **Identifying the formula options:**
- The question provides several formulas:
- Na2CO3 (Anhydrous Sodium Carbonate)
- Na2CO3.H2O (Sodium Carbonate Monohydrate)
- Na2CO3.7H2O (Sodium Carbonate Heptahydrate)
- Na2CO3.10H2O (Sodium Carbonate Decahydrate)

3. **Recognizing the concept of water of crystallization:**
- Water of crystallization refers to the water molecules that are chemically bound to a salt in a specific ratio. Each of the given formulas indicates a different number of water molecules associated with sodium carbonate.

4. **Determining the correct formula for Washing Soda:**
- Among the options, washing soda is specifically referred to as sodium carbonate decahydrate, which has 10 water molecules associated with it. Therefore, the correct formula for washing soda is Na2CO3.10H2O.

5. **Conclusion:**
- The formula of washing soda is Na2CO3.10H2O.

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