Correct Answer: Acid rain

Solution : The correct answer is Acid Rain.

Acid rain is rain with a lower pH than regular rain. This means it is more acidic and, as a result, can cause greater damage to stone and marble. Sulfuric acid and nitric acid are generated when sulphur dioxide (SO2) and nitrogen oxides (NOx) from power plants, industry, and cars mix with water in the atmosphere to form acid rain. These acids can then fall as rain, snow, fog, or dew to the earth. Acid rain may dissolve the calcium carbonate in stone and marble, causing it to discolour, degrade, and finally collapse. This is referred to as stone cancer.