Which of the following industries is the best source of increasing $CO$ levels in the atmosphere?

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

The conversion of hydroxyapatite occurs due to the presence of $F^{-}$ ions in water. The correct formula of hydroxyapatite is:

Green plants use carbon dioxide during photosynthesis and release oxygen,yet carbon dioxide is considered responsible for the greenhouse effect. Why?

Which of the following is the most significant air pollutant in modern times?

$A$ large number of fish are suddenly found floating dead on a lake. There is no evidence of toxic dumping,but you find an abundance of phytoplankton. Suggest a reason for the fish kill.