The major pollution-causing agent is:

Rice fields produce an important greenhouse gas. Name it.

Arrange the following in increasing order of their $BOD$ values: Sewage $(S)$,Distillery Effluent $(DE)$,Paper Mill Effluent $(PE)$,and Sugar Mill Effluent $(SE)$.

The Chernobyl tragedy occurred in

What do '$X$','$Y$',and '$Z$' represent in the given figure respectively?

In a pond near a village,a large number of fish suddenly die. Which of the following could be the reason for this?
$(a)$ Large amounts of urea and phosphate are used as fertilizers in nearby fields.
$(b)$ $DDT$ was sprayed in the entire area.
$(c)$ The pond water has become green and dirty.
$(d)$ The population of phytoplankton in the pond has decreased,reducing the photosynthetic capacity.
Which two of the above reasons are responsible?