Question

The anhydrous calcium sulphate is called.
A) Gypsum
B) Anhydrite
C) Plaster of paris
D) Lime

Answer 1

Anhydrous materials do not contain any water $(H_2O)$ molecules. Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula $CaSO_4$.

Complete answer:
Calcium is an essential metal for living organisms. Due to its chemical properties, it finds usage in the preparation of alloys as a deoxidizer, desulfurizer and decarbonizer. However, it is not just the metal itself, a number of calcium compounds are also crucial to several industries and are prepared on a large scale.
Some of them are calcium carbonate, calcium oxide (quick lime), calcium hydroxide, calcium sulphate, calcium chloride, etc.
The hydrate forms of $CaS{O_4}$ is plaster of paris and gypsum.
Plaster of Paris - $CaS{O_4}.{\dfrac{1}{2}}{H_2}O$ also known as hemihydrate.
Gypsum - $CaS{O_4}.2{H_2}O$ (dihydrate).
Lime is called calcium hydroxide with the chemical formula $Ca(OH)_2$.
The anhydrous calcium sulphate is called Anhydrite.
$CaS{O_4}$ is anhydrous state or anhydrite.

Thus option (B) is the correct answer.

Note: If the heating is at a higher temperature, gypsum loses all its water and becomes anhydrous calcium sulfate, ($CaS{O_4}$). Calcium sulphate is majorly used in the manufacturing of plaster of paris. It is also used in tofu as a coagulant.