Identify the pollutant gases largely responsible for the discoloured and lustreless nature of marble of the Taj Mahal.

The marble used in the Taj Mahal is mainly calcium carbonate, whose chemical formula is written as $$CaCO_3$$.

We begin by recalling that the lustre and bright white colour of fresh marble can be spoiled when it reacts with acidic pollutants present in the atmosphere. The most common gaseous pollutants that lead to acid formation are sulfur dioxide, written as $$SO_2$$, and nitrogen dioxide, written as $$NO_2$$.

First, let us see how $$SO_2$$ behaves. In moist air, $$SO_2$$ dissolves in water vapour and is oxidised to form sulfuric acid. Symbolically, the sequence proceeds as

$$SO_2 + H_2O \rightarrow H_2SO_3$$

and then, in the presence of atmospheric oxygen,

$$2\,H_2SO_3 + O_2 \rightarrow 2\,H_2SO_4.$$

The sulfuric acid so produced is strongly acidic and readily attacks the calcium carbonate of marble. We write the main reaction as

$$CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + CO_2 + H_2O.$$

The product $$CaSO_4$$ (calcium sulfate) is gypsum, which is dull, crumbly and lacks the smooth shine of the original marble. Thus the polished surface becomes discoloured and lustreless.

Next, we consider $$NO_2$$. In a similar fashion, nitrogen dioxide reacts with water to form a mixture of nitric and nitrous acids, which can be further oxidised. The key equation is

$$2\,NO_2 + H_2O \rightarrow HNO_2 + HNO_3.$$

The nitric acid $$HNO_3$$ produced attacks marble as follows:

$$CaCO_3 + 2\,HNO_3 \rightarrow Ca(NO_3)_2 + CO_2 + H_2O.$$

Calcium nitrate, $$Ca(NO_3)_2$$, being water-soluble, slowly washes away, leaving behind a rough, pitted, and yellow-brown surface that has lost its natural shine.

Therefore, the two principal gaseous pollutants that generate these acids—and consequently are largely responsible for the discolouration and loss of lustre of the Taj Mahal’s marble—are $$SO_2$$ and $$NO_2$$.

Comparing with the given options, we see that Option C lists exactly these two gases.

Hence, the correct answer is Option C.