The depletion of ozone in the stratosphere is caused by .......

$A$ farmer is using pesticides in his field. He uses the produce from his field as food for fish. He is told that the fish are not fit for human consumption because large amounts of pesticides were found in the fish cells. How is this possible? Explain.

Thermal power plants can lead to:

The main cause of air pollution in large cities is ........

State whether the following statements are true or false:
$(1)$ The concentration of oxygen in cold water is $100 \ ppm$.
$(2)$ If the concentration of dissolved oxygen in water is less than $6 \ ppm$,the growth of fish gets inhibited.

Match the items in Column-$I$ with the compounds in Column-$II$.

Column-$I$	Column-$II$
$(A)$ Acid rain	$(1)$ $CHCl_2-CHF_2$
$(B)$ Photochemical smog	$(2)$ $CO$
$(C)$ Combination with hemoglobin	$(3)$ $CO_2$
$(D)$ Depletion of ozone layer	$(4)$ $SO_2$
	$(5)$ Unsaturated hydrocarbons