Which gas is the fourth most abundant by volume in dry air?

Which gas is the fourth most abundant by volume in dry air?

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

Answer: (B)

The main idea is the actual composition of dry air by volume (which equals mole fraction for gases at the same temperature and pressure). Dry air is dominated by nitrogen and oxygen, with tiny amounts of argon and carbon dioxide. In terms of volume, nitrogen is the most abundant, followed by oxygen, then argon, and finally carbon dioxide. Carbon dioxide sits at about 0.04% by volume, while argon is around 0.9%. That makes carbon dioxide the fourth-most abundant gas in dry air. The term “dry” removes water vapor, which can vary with humidity, but the ranking among these non-condensing gases remains consistent.

The main idea is the actual composition of dry air by volume (which equals mole fraction for gases at the same temperature and pressure). Dry air is dominated by nitrogen and oxygen, with tiny amounts of argon and carbon dioxide. In terms of volume, nitrogen is the most abundant, followed by oxygen, then argon, and finally carbon dioxide. Carbon dioxide sits at about 0.04% by volume, while argon is around 0.9%. That makes carbon dioxide the fourth-most abundant gas in dry air. The term “dry” removes water vapor, which can vary with humidity, but the ranking among these non-condensing gases remains consistent.