What two elements make up 99% of dry air?

What two elements make up 99% of dry air?

• A. Hydrogen and Oxygen
• B. Nitrogen and Oxygen
• C. Argon and Nitrogen
• D. Carbon Dioxide and Nitrogen

Answer: (B)

Dry air is dominated by two gases that together make up about 99% of its composition. Those gases are nitrogen and oxygen. In Earth's atmosphere, nitrogen accounts for about 78% and oxygen about 21%, so combined they total roughly 99%. The term “dry air” excludes water vapor, so the remaining roughly 1% comes from trace gases like argon, carbon dioxide, neon, helium, and others. Hydrogen isn’t a major component, and argon, while present, is only a small fraction, which is why the pair of nitrogen and oxygen best explains why 99% is made up of those two elements.