The correct option is CaSO4·1/2H2O.
Explanation
Plaster of Paris is a chemical compound chemically known as calcium sulphate hemihydrate. It is prepared by heating Gypsum at a controlled temperature of 373 K, causing it to lose water molecules.
- CaSO4·1/2H2O is Correct: The chemical formula for Plaster of Paris is CaSO4·½H2O. It is called calcium sulphate hemihydrate because two formula units of CaSO4 share one molecule of water.
- CaSO4·2H2O is Incorrect: CaSO4·2H2O represents Gypsum. When Plaster of Paris is mixed with water, it rehydrates to form Gypsum, setting into a hard solid mass.
- CaCO3 is Incorrect: CaCO3 represents Calcium Carbonate, which is the primary component of limestone, chalk, and marble.
- Ca(OH)2 is Incorrect: Ca(OH)2 represents Calcium Hydroxide, commonly known as slaked lime.
Key Takeaway: Plaster of Paris (CaSO4·½H2O) is distinct from Gypsum (CaSO4·2H2O) by the amount of water of crystallization it contains.