Which pollutants are present in the troposphere?

Identify the correct statements from the following:
$i$. In the presence of $UV$ light,$CF_2Cl_2(g)$ gives chlorine free radicals which will react with $O_3(g)$ to form $O_2(g)$.
$ii$. Drinking water with $10 \ ppm$ fluoride is better than drinking water with $1 \ ppm$ fluoride.
$iii$. The maximum permissible concentration of lead in drinking water is $50 \ ppb$.

The ions of $Ni, Hg, Ag, Pb, Zn$ etc.,are generated as waste from which industry?

How is nitrogen oxide formed in the atmosphere,and why is an excessive amount of nitrogen oxide harmful?

$BOD$ stands for:

What is green chemistry?