Plaster of Paris (POP) is

The correct option is CaSO₄ 1/2H₂O.

Detailed Explanation:

Plaster of Paris (commonly abbreviated as POP) is chemically known as calcium sulfate hemihydrate. The term "hemihydrate" refers to the presence of half a molecule of water of crystallization for every molecule of calcium sulfate (CaSO₄).

Its chemical formula is written as:
${\text{CaSO}}_4·\frac{1}{2}{\text{H}}_2\text{O}$
This representation means that two formula units of calcium sulfate share one molecule of water of crystallization, which can also be represented as 2CaSO₄·H₂O.

Plaster of Paris is prepared by heating gypsum (calcium sulfate dihydrate, CaSO₄·2H₂O) to a temperature of about 373 K (100 °C) in a kiln. At this temperature, gypsum loses three-fourths of its water of crystallization to form the hemihydrate:

${\text{CaSO}}_4·2{\text{H}}_2\text{O}\Rightarrow {\text{CaSO}}_4·\frac{1}{2}$

Therefore, the formula corresponding to Plaster of Paris is indeed CaSO₄ 1/2H₂O.