Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Gypsum is used for making fireproof wall boards.
Reason (R): Gypsum is unstable at high temperatures.
In the light of the above statements, choose the correct answer from the options given below:

Assertion (A): Gypsum is used for making fireproof wall boards.

This is CORRECT. Gypsum ($$CaSO_4 \cdot 2H_2O$$) is widely used in making fireproof wall boards (drywall/gypsum board) because of its fire-resistant properties.

Reason (R): Gypsum is unstable at high temperatures.

This is CORRECT. When exposed to high temperatures, gypsum undergoes dehydration:

$$ CaSO_4 \cdot 2H_2O \xrightarrow{\Delta} CaSO_4 \cdot \frac{1}{2}H_2O + \frac{3}{2}H_2O $$

This endothermic dehydration process absorbs heat, which slows down the spread of fire. The water released as steam also helps in fire suppression.

R is the correct explanation of A because it is precisely the instability of gypsum at high temperatures (releasing water endothermically) that makes it effective as a fireproof material.

Therefore, both (A) and (R) are correct and (R) is the correct explanation of (A).