Which of the following gases causes depletion in the ozone layer?

Which of the following is a secondary pollutant?

$A$ large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping,but you find an abundance of phytoplankton. Suggest a reason for the fish kill.

In municipal sewage,$BOD$ values (in $ppm$) are

What is the full form of $COD$?

Which is the main component responsible for acid rain in the atmosphere?