Which gas is most abundant in Earth's atmosphere?

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

Answer: (B)

In Earth's atmosphere the most abundant gas is nitrogen. It makes up about 78% of dry air, while oxygen is around 21%, and the rest are trace gases like argon and carbon dioxide. Nitrogen is so abundant because it is fairly inert at room temperature and pressure, so it doesn’t easily react to form compounds that would remove it from the air. Oxygen, on the other hand, is more reactive and participates in many processes, which keeps its amount lower than nitrogen. That’s why, despite oxygen being important for life, nitrogen remains the dominant component of the atmosphere.