Taj Mahal is being slowly disfigured and discolored. This is primarily due to:
(A) Water pollution
(B) Global warming
(C) Soil pollution
(D) Acid rain

Hint: Taj Mahal is being slowly disfigured and discolored due to the formation of calcium sulphate. The calcium sulphate is more soluble in water as compared to calcium carbonate so it easily gets washed out.

Complete step by step solution:
Acid rain is precipitation that has the pH which is less than that of the pH of natural rainwater. This is the reason behind the stiffness of flower buds. The pH determines whether the solution is acidic or basic. The process of combustion produces carbon monoxide, nitrogen oxide. These gases contribute to air pollution. When sulphur dioxide and the nitrogen oxides present in the atmosphere mix with water vapours, it forms Sulphuric acid or nitric acid or it leads to acid rain. Taj Mahal is being slowly disfigured and discolored due to the reaction of calcium carbonate i.e. marble with the Sulphuric acid and nitric acid present in the rain and form calcium sulphate which is more soluble than calcium carbonate. This results in the erosion of the beautiful monument. The reaction involved is:
\[CaC{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\to CaS{{O}_{4}}+C{{O}_{2}}+{{H}_{2}}O\]

Hence the correct answer is (D) acid rain.

Additional information:
Acid rain have several harmful effects such as:
It increases the pH of the water bodies which make it difficult for the survival of the aquatic animals. It affects the food chain It also causes harm to the forests by damaging the leaves of the trees and by removing the nutrients from the soil. It makes it hard for the trees to take up water through the steam.

Note: By designing a cleaner power plant we can prevent air pollution. And if we reduce the use of fossil fuel, we can reduce the emission of harmful pollutants which leads to the acid rain.