Explanation:

Plaster of Paris (POP) is a white powdery chemical compound that hardens when mixed with water. Its chemical name is calcium sulfate hemihydrate. The 'hemihydrate' indicates that for every two molecules of calcium sulfate, there is one molecule of water of crystallization. Its chemical formula is $\text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O}$. Option (A) is correct as it accurately describes the chemical composition of Plaster of Paris. Option (B) is incorrect; Calcium Sulphate dihydrate ($\text{CaSO}_4 \cdot 2\text{H}_2\text{O}$) is gypsum, the raw material from which Plaster of Paris is made by heating. Option (C) is incorrect; Calcium hydroxide ($\text{Ca(OH)}_2$) is slaked lime, a different compound used in construction and agriculture. Option (D) is incorrect; Calcium chloride ($\text{CaCl}_2$) is a salt commonly used as a desiccant or for de-icing, and is not Plaster of Paris.