Solution:
∙ The major threat to the Taj Mahal is acid rain. When acid rain falls on the Taj, which is completely made of marble, it reacts with marble to form a powder-like substance which is then washed away by the rain. This phenomenon is known as marble cancer. (1 mark)
∙ In addition, the soot particles emitted from the Mathura oil refineries located near Agra are contributing to the yellowing of the Taj Mahal marble. (1 mark)