When did the worst environmental nuclear power plant accident and the $MIC$ gas tragedy occur,respectively?

Match the following columns.

Column-$I$	Column-$II$
$(p)$ $CFC$	$(v)$ Troposphere
$(q)$ Bad ozone	$(w)$ Plastic
$(r)$ Good ozone	$(x)$ Ozone depletion is occurring widely
$(s)$ Non-biodegradable waste	$(y)$ Stratosphere
	$(z)$ Paper,leaf

Consider the following statements about eutrophication:
$I.$ Eutrophication is the natural ageing of a water body by nutrient enrichment.
$II.$ The accelerated ageing of lakes due to sewage and agricultural and industrial wastes is called cultural or accelerated eutrophication.
$III.$ The plant nutrients responsible for eutrophication are nitrates and phosphates.
$IV.$ Phosphates and nitrates accelerate the growth of algae which utilize oxygen and may deoxygenate the water enough to kill the fish and other aquatic animals.
Which of the statements given above are correct?

Identify the correct statements from the following:
$(i)$ $DDT$ is non-biodegradable.
$(ii)$ Heavy metals are responsible for biomagnification.
$(iii)$ High concentration of $DDT$ disturbs calcium metabolism in birds.
$(iv)$ The concentration of $DDT$ in large fish can be up to $2 \, ppm$.

Arrange $CFC, CH_4, N_2O$ and $CO_2$ in decreasing order according to their contribution in the greenhouse effect.

What are the side effects of heavy and constant grazing?