Which of the following is responsible for photochemical smog?

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 $50 \ ppb$.

What is the troposphere,and which components are present in it?

What is Biochemical Oxygen Demand $(BOD)$?

The living organisms or the surroundings of the earth's composition are known as .....

Explain the effects of acid rain on the Taj Mahal.