Which of the following is not a conventional source of energy?

The concentration of an insecticide in the animals of a species is called:

The most densely populated city in India is

Which of the following strategies is not useful for mitigating global warming?

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?

Domestic sewage contains nutrients like nitrogen and phosphorus which favours the excessive growth of planktonic (free-floating) algae which can accelerate which of the following phenomenon?