Which list contains gases found only in "clean" air? A. carbon dioxide, nitrogen dioxide, sulfur dioxide, helium
B. helium, methane, carbon dioxide, xenon
hydrogen, oxygen, chlorine, ammonia
C. argon, neon, krypton, radon
D. fluorine, chlorine, bromine, iodine

hydrogen, oxygen, chlorine, ammonia

Explanation:

Air is a mixture of gases. When we say "clean" air here, we are referring to air that does not contain pollutant gases.

Some components of air such as water vapour, methane, CO2, and N2O are greenhouse gases. They are known to contribute towards global warming.

Some gases such as SO2 and NO2 contribute towards acid rain. The oxides of nitrogen are particularly involved in the formation of photochemical smog.

The halogens are known to lead to the depletion of the ozone layer and radon is a radioactive gas.

Hence, hydrogen, oxygen, chlorine, ammonia have no negative environmental impact hence they are found in clean air.