Question

Which salts are responsible for the yellow colour of Taj Mahal in Agra due to acid rain?
a.) $CaC{l_2}$ and $CaS{O_4}$
b.) $Ca{(N{O_3})_2}$ and $CaS{O_4}$
c.) $Ca{(N{O_3})_2}$ and $BaS{O_4}$
d.) $CaS{O_4}$ and $BaC{l_2}$

Answer 1

Hint: The nitric acid and sulphuric acid are the components of acid rain. These react with Calcium carbonate present in white marble of Taj Mahal and as a result of chemical reaction form nitrates and sulphates of calcium which turns the white marble into yellow.

Complete step by step answer:
First, let us see what acid rain is.
The Sulphur and nitrogen oxides reach the upper atmosphere and mix with water forming nitric acid and sulphuric acid and then come down on the surface of the earth with precipitation. This is called acid rain.
The white marble of Taj Mahal in Agra is composed of Calcium. Whenever there is acid rain in Agra, the nitric acid and sulphuric acid come along with precipitates.
These acids react with calcium carbonate of marble to form calcium sulphate and calcium nitrate along with carbon dioxide and water.
The react for these processes can be written as -
$\begin{gathered}
CaC{O_3} + 2HN{O_3} \to Ca{(N{O_3})_2} + C{O_2} + {H_2}O \\
CaC{O_3} + {H_2}S{O_4} \to CaS{O_4} + C{O_2} + {H_2}O \\
\\
\end{gathered} $
These calcium nitrate and calcium sulphate formed is responsible for the yellowing of the white marble.
Thus, option b.) is the correct answer.

Note: Marble is composed of carbonate minerals, normally calcite and dolomite. Barium is not present in marbles which form the Taj Mahal. So, the options containing barium are removed.
The acid rain has a pH of less than 5.6. It has adverse effects on the animal skin, marbles and agriculture etc.