The number of water molecules present in one formula unit of gypsum is 2.
✅ Correct answer: 2
Explanation: The chemical formula of gypsum is CaSO₄·2H₂O, which means each formula unit of gypsum contains 2 water molecules of crystallization.
The correct answer is 2. Gypsum has the chemical formula CaSO4·2H2O, which indicates that each formula unit of gypsum contains two water molecules. Thus, the number of water molecules present in one formula unit of gypsum is 2.