Distinguishing Natural Air Components from Pollutants

Steps:

• Define atmospheric pollutants as gases harmful to health or environment when emitted in excess from human activities.
• Evaluate neon (1): inert noble gas, naturally occurring in trace amounts, non-toxic and non-reactive.
• Evaluate carbon monoxide (2): toxic byproduct of incomplete combustion, causes respiratory issues and is regulated as a pollutant.
• Evaluate nitrogen (3): primary air component (78%), essential and non-polluting in natural concentrations.
• Evaluate methane (4): potent greenhouse gas from sources like agriculture and leaks, contributes to global warming as a pollutant.

Why C is correct:

• Carbon monoxide and methane are classified as criteria air pollutants by agencies like the EPA due to their adverse health and climate impacts.

Why the others are wrong:

• A: Neon is harmless and not a pollutant.
• B: Both neon and nitrogen are benign natural gases.
• D: Nitrogen is a major, non-polluting air constituent.

Final answer: C