Question

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Many of the world's historic buildings, monuments and statues are degraded/defaced due to exposure to acidic rain water.
Reason R: Reaction between limestone and sulphuric acid in rain water produces water soluble product Gypsum which is easily washed away and leave behind pitted surface.

• A. Both A and R are correct and R is the correct explanation of A.
• B. Both A and R are correct but R is NOT the correct explanation of A.
• C. A is correct but R is not correct.
• D. A is not correct but R is correct.

Hint:

Chemical reaction to remember: $CaCO_3 \text{ (Limestone)} + H_2SO_4 \text{ (Acid Rain)} \rightarrow CaSO_4 \text{ (Gypsum)} + H_2O + CO_2$. The loss of solid $CaCO_3$ is what causes the visible "pitting."

Answer 1

The Correct Option is A

Concept: Acid rain (typically containing $H_2SO_4$ and $HNO_3$) causes significant chemical weathering of stone materials, especially those containing calcium carbonate ($CaCO_3$), such as limestone and marble.

Step 1: Evaluating the Assertion.
It is a well-documented global issue that historic monuments (like the Taj Mahal or the Parthenon) suffer from "stone cancer." Acidic pollutants in rain react with the stone, leading to erosion, discoloration, and structural weakening. Thus, Assertion A is correct.

Step 2: Evaluating the Reason and Connection.
Limestone is primarily $CaCO_3$. When it reacts with the sulfuric acid ($H_2SO_4$) in acid rain, it forms Gypsum ($CaSO_4 \cdot 2H_2O$). Unlike limestone, gypsum is relatively soft and water-soluble. When rain falls, it dissolves the gypsum layer, washing it away and revealing a damaged, "pitted" surface. Thus, Reason R is correct and directly explains the mechanism behind Assertion A.