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:

We need to evaluate the Assertion-Reason pair about gypsum.

Evaluate Assertion (A)

Assertion: Gypsum is used for making fireproof wall boards.

This is correct. Gypsum ($$CaSO_4 \cdot 2H_2O$$) is widely used in fireproof wall boards (drywall). When exposed to fire, gypsum releases its water of crystallization, which absorbs heat and slows the spread of fire.

Evaluate Reason (R)

Reason: Gypsum is unstable at high temperatures.

This is correct. At high temperatures, gypsum decomposes: it first loses water to form plaster of Paris ($$CaSO_4 \cdot \frac{1}{2}H_2O$$), and at even higher temperatures forms anhydrous calcium sulfate. This decomposition is endothermic.

Check if R explains A

The instability of gypsum at high temperatures (endothermic decomposition releasing water vapor) is precisely why it is effective as a fireproof material. The heat absorption during decomposition delays the temperature rise on the protected side. Therefore, R is the correct explanation of A.

The answer is Option D: Both (A) and (R) are correct and (R) is the correct explanation of (A).