The number of water of crystallisation in hypo are____.

Answer

To solve the question regarding the number of water of crystallization in hypo, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Water of Crystallization**:
- Water of crystallization refers to the fixed number of water molecules that are associated with one formula unit of a salt. This water is integral to the structure of the salt and is usually present in a specific ratio.

2. **Identify the Chemical Formula of Hypo**:
- The compound referred to as "hypo" is sodium thiosulfate, which has the chemical formula Na2S2O3.5H2O.

3. **Analyze the Formula**:
- In the formula Na2S2O3.5H2O, the "5H2O" indicates that there are 5 water molecules associated with each formula unit of sodium thiosulfate.

4. **Count the Water Molecules**:
- From the formula, we can see that there are 5 water molecules (5H2O) present.

5. **Conclude the Answer**:
- Therefore, the number of water of crystallization in hypo is 5.

### Final Answer:
The number of water of crystallization in hypo is **5**.

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