AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt (e.g., CuSO₄·5H₂O contains 5 water molecules).
Source: Chapter 2, What you have learnt
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The examiner expects the exact definition from the textbook. The key phrase is "fixed number of water molecules" in "one formula unit of a salt" — both parts are needed for full marks. Adding a familiar example (like copper sulphate) strengthens the answer but is not compulsory for 1 mark.