Plaster of Paris is prepared by heating one of the following to a temperature of ${100}^{o}C$. This is :

(a) $CaS{O}_{3}2H_{2}O$

(b) $CaC{l}_{2}2H_{2}O$

(c) $CaC{O}_3.2H_{2}O$

(d) $CaS{O}_4.2H_{2}O$

Plaster of Paris is prepared by heating gypsum [which is chemically calcium sulphate dihydrate ($CaS{O}_4.2H_{2}O$) at 373 K. On heating at 373 K, gypsum loses water molecules and becomes Plaster of Paris, which has the chemical name calcium sulphate hemihydrate. Its chemical formula is $CaS{O}_4.\frac{1}{2}{H}_{2}O$. Following is the chemical equation for the reaction

$\underset{\text{Gypsum}}{CaS{O}_4.2H_{2}O}\stackrel{373K}{\to }\underset{\text{Plaster of Paris}}{CaS{O}_4.\frac{1}{2}{H}_{2}O}+\frac{3}{2}{H}_{2}O$