In recent years, there has been some concern over the threat posed by the Mathura Oil Refinery and the thermal power plants to the Taj Mahal in Agra. The scientific basis of any possible damage to the Taj is mainly

Answer: (b) acid precipitation and tropospheric ozone

SO₂ and NOₓ from the refinery and power plants form sulphuric and nitric acid in rain, and marble (calcium carbonate) reacts and flakes: “marble cancer”. Ground-level (tropospheric) ozone, formed from NOₓ in sunlight, also attacks the surface.

The idea

Marble is calcium carbonate. Acid reacts with it and turns the surface into calcium sulphate (gypsum), which is soft, dull and flakes off. This is called marble cancer.

Refinery and power plants burn fuel → Sulphur dioxide and nitrogen oxides rise → They form sulphuric and nitric acid in moist air → Acid falls on the marble → Marble surface turns to gypsum and flakes

Why the others are wrong

(a) Stratospheric ozone is 15–35 km up and protects us, and CFCs destroy it. That is not what eats marble at ground level.

(c) CO₂-driven warming is a global problem. It does not explain local damage to the Taj.

(d) UV at 240–260 nm is absorbed high in the atmosphere, and Yamuna fumes are not the scientific basis here.

The trap

Option (a) has the word “ozone”, but the wrong layer. For the Taj it is ground-level (tropospheric) ozone, not the stratospheric ozone layer.

Also know

In M.C. Mehta v. Union of India (1996), the Supreme Court acted on the Taj Trapezium Zone, about 10,400 km² around the Taj, where coal-using industries had to switch to gas or move out. Today’s yellowing is also caused by particulate matter (black and brown carbon), which the ASI removes with a clay pack of multani mitti.