Which of the following is a biodegradable pollutant?

Due to biomagnification,if the concentration of $DDT$ in water is $0.003 \, ppm$,what will be the concentration of $DDT$ in zooplankton,small fish,large fish,and fish-eating birds,respectively?

Match the columns:

Column-$I$	Column-$II$
$(1)$ Mercury	$(a)$ Low blood pressure,blindness
$(2)$ Lead	$(b)$ Hyperkeratosis,liver cirrhosis
$(3)$ Arsenic	$(c)$ Bone deformation,testicular atrophy
$(4)$ Cadmium	$(d)$ Abdominal pain,haemolysis
	$(e)$ Anaemia,convulsions

In an area where $DDT$ had been used extensively,the population of birds declined significantly because

At what level does noise become harmful noise pollution?

In areas where $DDT$ is used extensively,the bird population declines significantly because...