Question

: Identify the pollutant gases largely responsible for the discoloured and lusterless nature of marble of the Taj Mahal.
A.${\text{C}}{{\text{O}}_{\text{2}}}$ and ${\text{N}}{{\text{O}}_{\text{2}}}$
B.${\text{S}}{{\text{O}}_{\text{2}}}$ and ${\text{N}}{{\text{O}}_{\text{2}}}$
C.${{\text{O}}_3}$ and ${\text{C}}{{\text{O}}_{\text{2}}}$
D.${\text{S}}{{\text{O}}_{\text{2}}}$ and ${{\text{O}}_3}$

Answer 1

Hint: The pollutant gases responsible for the discolouration of marble of the Taj Mahal are oxides of sulphur and nitrogen. The discolouration of marble in buildings is mainly caused by acid rain which consists of so many acids where the ratio of the oxides of sulphur and nitrogen plays a key role.

Complete step by step answer:
Acid rain literally indicates the presence of excessive acids in rainwater. Sulphur and nitrogen when burnt in atmospheric oxygen, get converted into sulphur dioxide and nitrogen dioxide respectively, which are highly soluble in water.
${\text{S + }}{{\text{O}}_{\text{2}}} \to {\text{S}}{{\text{O}}_{\text{2}}}$
Sulphur dioxide further gets converted into sulphur trioxide.
$2{\text{S}}{{\text{O}}_2}{\text{ + }}{{\text{O}}_{\text{2}}} \to 2{\text{S}}{{\text{O}}_3}$
In case of nitrogen, the following reactions take place.
${\text{NO}} + {{\text{O}}_3} \to {\text{N}}{{\text{O}}_{\text{2}}} + {{\text{O}}_{\text{2}}}$
The nitrogen dioxide again gets converted into nitrogen trioxide which ultimately reacts with the nitrogen dioxide and gets converted into dinitrogen pentoxide.
${\text{N}}{{\text{O}}_2}{\text{ + }}{{\text{O}}_3} \to {\text{N}}{{\text{O}}_3} + {{\text{O}}_{\text{2}}}$
${\text{N}}{{\text{O}}_3} + {\text{N}}{{\text{O}}_2} \to {{\text{N}}_2}{{\text{O}}_5}$
Sulphur trioxide in a humid atmosphere forms droplets of sulphuric acid.
${\text{S}}{{\text{O}}_{\text{2}}} + \dfrac{1}{2}{{\text{O}}_{\text{2}}} + {{\text{H}}_{\text{2}}}{\text{O}}\xrightarrow{{{\text{NO}}}}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}$
Under the humid conditions of air, dinitrogen pentoxide reacts with water vapour to form droplets of nitric acid.
${{\text{N}}_2}{{\text{O}}_5} + {{\text{H}}_{\text{2}}}{\text{O}} \to {\text{2HN}}{{\text{O}}_{\text{3}}}$
Some nitrous acid is also formed. The nitric acid and nitrous acid form then return to the earth’s surface.
Sulphuric acid, nitric acid thus formed combines with hydrochloric acid to generate precipitation which is commonly referred to as acid rain.
This acid rain causes extensive damage to buildings and structural materials of marble, limestone etc. Marble contains calcium carbonate which reacts with acid to give carbon dioxide and water. The attack on marble is called stone leprosy.
${\text{CaC}}{{\text{O}}_{\text{3}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}} \to {\text{CaS}}{{\text{O}}_{\text{4}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O + C}}{{\text{O}}_{\text{2}}}$
Hence, the marble of the Taj Mahal in Agra is losing its luster and colour due to ${\text{S}}{{\text{O}}_{\text{2}}}$ and ${\text{N}}{{\text{O}}_{\text{2}}}$

Hence option B is correct.

Note:
Acid rain is also very dangerous to the living organisms as it can destroy life. Acidification can cause havoc in the human nervous system, respiratory system as well as the digestive system by making the human body an easy prey to neurological diseases. This happens because these acids form highly toxic compounds which contaminate the portable water and enter the human body.