To which class of pesticides do $DDT$,$BHC$,aldrin,and endosulphan belong?

Explain pollution caused by automobiles and how the use of a catalytic converter in them reduces pollution.

Is it true that if the dissolved oxygen level drops to zero,the water will become septic? Give an example which could lower the dissolved oxygen content of an aquatic body.

What are the various components of domestic sewage? Discuss the effects of discharging sewage into a river.

Which one of the following is the heavy toxic metal present in waste water from industries?

Prolonged liberal irrigation of agricultural fields is likely to create the problem of