Answer: CaCO 3 + H 2 SO 4 → CaSO 4 + H 2 O + CO 2.
- A CaCO<sub>3</sub> + H<sub>2</sub>SO<sub>4</sub> → CaSO<sub>4</sub> + H<sub>2</sub>O + CO<sub>2</sub>
- B CaCO<sub>3</sub> + 2HCl → CaCl<sub>2</sub> + H<sub>2</sub>O + CO<sub>2</sub>
- C CaCO<sub>3</sub> + H<sub>2</sub>SO<sub>3</sub> → CaSO<sub>3</sub> + H<sub>2</sub>O + CO<sub>2</sub>
- D CaCO<sub>3</sub> + CO<sub>2</sub> + H<sub>2</sub>O → Ca(HCO<sub>3</sub>)<sub>2</sub>
Correct answer: A. CaCO<sub>3</sub> + H<sub>2</sub>SO<sub>4</sub> → CaSO<sub>4</sub> + H<sub>2</sub>O + CO<sub>2</sub>
Explanation: Sulphuric acid from acid rain reacts with marble (CaCO<sub>3</sub>) to produce calcium sulphate (gypsum), water, and CO<sub>2</sub>. Gypsum is soft, powdery, and partly soluble, so it crumbles away from the surface - a process known as 'stone cancer'. This is the specific reaction threatening the Taj Mahal's marble.
Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.
Concept context
Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.