Which one of the following is the chemical formula of gypsum?
A
$$CaS{O_4} \cdot 2{H_2}O$$
B
Ca<sub>2</sub>SiO<sub>4</sub>
C
$$2CaS{O_4} \cdot {H_2}O$$
D
CaSO<sub>4</sub>
Correct Answer: $$CaS{O_4} \cdot 2{H_2}O$$