The acid that is believed to be mainly responsible for the damage of the Taj Mahal is ...

The enamel present on teeth becomes much harder due to the conversion of $[3 Ca_3(PO_4)_2, X]$ into $[3 Ca_3(PO_4)_2, Y]$. What are $X$ and $Y$?

Biosphere refers to

The chlorine free radical reacts with ozone to form a ..... free radical.

Given below are two statements:
Statement $I:$ Classical smog occurs in cool humid climate. It is a reducing mixture of smoke,fog and sulphur dioxide.
Statement $II:$ Photochemical smog has components,ozone,nitric oxide,acrolein,formaldehyde,$PAN$ etc.
In the light of above statements,choose the most appropriate answer from the options given below:

The type of pollution that increases during the daytime and in the presence of $O_{3}$ is