Which four gases are the main components of Earth's atmosphere by abundance?

• A. Nitrogen, Oxygen, Argon, Carbon Dioxide
• B. Nitrogen, Oxygen, Neon, Helium
• C. Nitrogen, Oxygen, Water Vapor, Methane
• D. Hydrogen, Oxygen, Nitrogen, Argon

Answer: (A)

The atmosphere is led by two gases that make up the vast majority of the air: nitrogen and oxygen. Nitrogen accounts for about 78% of dry air, and oxygen about 21%. After these, the next most abundant gases are present in much smaller, but relatively steady, amounts: argon and carbon dioxide. Argon is roughly 0.9%, and carbon dioxide is around 0.04% in dry air. Water vapor can vary widely by location and weather, so it isn’t treated as a fixed main component. Neon, helium, hydrogen, and many other gases are present only in trace amounts. So, the four most abundant gases by volume are nitrogen, oxygen, argon, and carbon dioxide.