The greenhouse effect is caused by ...... .

Why is it safer to use soap from the environmental point of view?

Acid rain is mainly caused by the emissions of which of the following gases?
$I.$ Sulphur dioxide
$II.$ Carbon dioxide
$III.$ Nitrogen dioxide
$IV.$ Methane

The insecticide $DDT$ is considered as . . . . . .

Given below are two statements :-
Statement $I :$ The value of the parameter "Biochemical Oxygen Demand $(BOD)$" is important for survival of aquatic life.
Statement $II :$ The optimum value of $BOD$ is $6.5 \ ppm$.
In the light of the above statements,choose the most appropriate answer from the options given below:

Ultraviolet radiation is absorbed by