The secondary precursors of photochemical smog are

Which gas contributes the least to global warming?

Photochemical smog consists of an excessive amount of $X$,in addition to aldehydes,ketones,peroxyacetyl nitrate $(PAN)$,and so forth. $X$ is

Fill in the blanks:
$(1)$ Carbon dioxide is found in the ................. layer.
$(2)$ $A$ high concentration of carbon dioxide is responsible for ................. .
$(3)$ ................. gas is used in air conditioners.
$(4)$ Acid rain causes damage to the ................. monument (wonder).

Which of the following statements are correct?
a) $F^{-}$ ion concentration above $2 \ ppm$ causes brown mottling of teeth
b) The maximum limit of nitrate in drinking water is $400 \ ppm$
c) Depletion of ozone layer leads to cataract and skin cancer
d) The irritant red haze in the traffic is due to oxides of sulphur

Write down the reactions involved during the formation of photochemical smog.