Concept: Trace gases exist in tiny amounts, but some can strongly influence climate.
Explanation: Carbon dioxide,
CO2, is a trace gas because it makes up less than
0.04% of the atmosphere.
However, it plays a major role in the greenhouse effect by absorbing infrared heat radiated from the Earth's surface.
This absorbed heat is trapped in the atmosphere, causing global warming.
Oxygen and nitrogen make up most of the air, but they do not trap heat effectively.
Argon is also an unreactive gas with no significant heat-trapping ability.
Answer: C. Carbon dioxide