Assertion: Plaster of paris is calicum sulphate hemihydrate [CaSO₄.\(\frac{1}{2}\)H₂O] and Gypsum is Calcium sulphate dihydrate [CaSO₄.2H₂O].

Reason: Plaster of Paris is a white powder and on mixing with water, it changes to gypsum.

Choose the correct answer from the following options.

Both Assertion and Reason are correct, and Reason is the correct explanation of Assertion.

The correct answer is option 1. Both Assertion and Reason are correct, and Reason is the correct explanation of Assertion.

On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO₄.\(\frac{1}{2}\)H₂O). This is called Plaster of Paris, the substance which doctors use as plaster for supporting fractured bones in the right position.

Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass (Gypsum-CaSO₄.2H₂O).

CaSO₄.\(\frac{1}{2}\)H₂O + \(\frac{1}{2}\)H₂O → CaSO₄.2H₂O