Which of the following is not considered to be a pollutant?

Which of the following statements about smog is/are correct?
$(i)$ Smog formed on sunny days contains oxidizing molecules.
$(ii)$ Photochemical smog contains many reactive molecules.
$(iii)$ The main polluting components of smog are oxides of carbon.
$(iv)$ The presence of carbon monoxide in air leads to the formation of ozone in smog.

Recent reports of acid rain in industrial cities are due to the effect of atmospheric pollution by

The conversion of sulfur dioxide to sulfur trioxide in the absence of a catalyst is a slow process. However,this process occurs easily in the atmosphere. Describe how this happens and write the chemical equations for the formation of $SO_3$ from $SO_2$.

The consequence of global warming may be the following:

Use of chlorofluorocarbons is not encouraged because