Which one of the following is responsible for turning Taj Mahal yellow?

The correct option is Sulphur dioxide.

Step-by-Step Explanation:

1. Acid Rain Formation: Power plants, refineries, and automotive exhausts in industrial regions emit high levels of gases such as sulphur dioxide (${\mathrm{SO}}_2$) and nitrogen dioxide (${\mathrm{NO}}_2$) into the atmosphere.

2. Chemical Reaction: When sulphur dioxide reacts with water vapour and oxygen present in the atmosphere, it forms sulphuric acid ($H_2{\mathrm{SO}}_4$):

$2{\mathrm{SO}}_2+O_2+2H_{2}O\to 2H_2{\mathrm{SO}}_4$

3. Discoloration of Marble: The Taj Mahal is constructed primarily of white marble, which consists of calcium carbonate (${\mathrm{CaCO}}_3$). When acid rain containing sulphuric acid reacts with marble, it converts calcium carbonate into calcium sulphate (${\mathrm{CaSO}}_4$):

${\mathrm{CaCO}}_3+H_2{\mathrm{SO}}_4\to {\mathrm{CaSO}}_4+H_{2}O+{\mathrm{CO}}_2$

4. Conclusion: This chemical reaction, along with the accumulation of suspended particulate matter (soot and dust), leads to the corrosion and yellowing of the iconic white marble, a phenomenon commonly known as "Marble Cancer". Therefore, sulphur dioxide is primarily responsible for turning the Taj Mahal yellow.