Atmosphere of Earth composition: what are the major gases?

Atmosphere of Earth composition: what are the major gases?

• A. 78% nitrogen, 21% oxygen, 1% inert gas
• B. 50% nitrogen, 50% oxygen
• C. 100% nitrogen
• D. 60% oxygen, 40% nitrogen

Answer: (A)

Air is mostly nitrogen and oxygen by volume. In dry air, nitrogen makes up about 78%, oxygen about 21%, and the remaining roughly 1% consists of noble and other trace gases such as argon, neon, helium, krypton, hydrogen, carbon dioxide, and others. That combination—approximately 78% N2, 21% O2, and about 1% other gases—best matches the actual atmospheric composition. The other options either misstate the proportions or imply improbable ratios (like all nitrogen or an equal split), which does not reflect how Earth's atmosphere is formed.

Air is mostly nitrogen and oxygen by volume. In dry air, nitrogen makes up about 78%, oxygen about 21%, and the remaining roughly 1% consists of noble and other trace gases such as argon, neon, helium, krypton, hydrogen, carbon dioxide, and others. That combination—approximately 78% N2, 21% O2, and about 1% other gases—best matches the actual atmospheric composition. The other options either misstate the proportions or imply improbable ratios (like all nitrogen or an equal split), which does not reflect how Earth's atmosphere is formed.