The correct option is CaSO4·2H2O.
Explanation
Gypsum is a naturally occurring mineral and a hydrated salt of calcium. Chemically, it is known as calcium sulfate dihydrate. It is widely used in the manufacturing of cement, plaster, and wallboard.
Analysis of Options:
- CaSO4·2H2O is Correct: The chemical formula CaSO4·2H2O represents calcium sulfate dihydrate, commonly known as gypsum. The "2H2O" indicates the presence of two water molecules of crystallization per formula unit of calcium sulfate.
- CaSO4·H2O is Incorrect: CaSO4·H2O represents calcium sulfate monohydrate, which is not the standard formula for naturally occurring gypsum.
- CaSO4·1/2H2O is Incorrect: CaSO4·1/2H2O represents calcium sulfate hemihydrate, commonly known as Plaster of Paris. This substance is obtained by heating gypsum at 373 K, causing it to lose water molecules.
- CaSO3·2H2O is Incorrect: CaSO3·2H2O represents calcium sulfite dihydrate, which is chemically distinct from the sulfate found in gypsum.
Key Takeaway:
Gypsum is CaSO4·2H2O (dihydrate), whereas Plaster of Paris is CaSO4·1/2H2O (hemihydrate). The transition between the two involves the loss or gain of water of crystallization.