Anhydrous substance is the one that does not contain ..................

Answer

**Step-by-Step Solution:**

1. **Understanding Anhydrous Substances**:
- An anhydrous substance is defined as one that does not contain water. The prefix "an-" means "without," and "hydrous" refers to water.

2. **Differentiating Between Hydrated and Anhydrous Substances**:
- Hydrated substances are those that have water molecules incorporated into their structure, often referred to as water of crystallization.
- Anhydrous substances, on the other hand, are those from which this water has been removed.

3. **Defining Water of Crystallization**:
- Water of crystallization is the water that is part of the crystalline structure of certain compounds. It is essential for maintaining the structure of hydrated salts.

4. **Example of Hydrated and Anhydrous Substances**:
- A common example is copper(II) sulfate, which can exist as CuSO4·5H2O (hydrated) and CuSO4 (anhydrous). When heated, the hydrated form loses its water of crystallization and becomes anhydrous.

5. **Conclusion**:
- Therefore, the answer to the question is: An anhydrous substance is one that does not contain water of crystallization.

**Final Answer**: Anhydrous substance is the one that does not contain **water of crystallization**.

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