What are the main components of Earth's atmosphere?

What are the main components of Earth's atmosphere?

• A. Oxygen (~78%) and nitrogen (~21%), with small amounts of argon, carbon dioxide, neon, etc.
• B. Nitrogen (~78%) and oxygen (~21%), with small amounts of argon, carbon dioxide, neon, etc.
• C. Argon (~1%) and neon, etc.
• D. Helium is a major component.

Answer: (B)

The main idea is recognizing which two gases dominate Earth's atmosphere. Dry air is mostly nitrogen and oxygen, with nitrogen making up about 78% and oxygen about 21%. The rest—argon, carbon dioxide, neon and other trace gases—tresents only a small fraction. This makes nitrogen the most abundant gas and oxygen the second most abundant, which is why a statement listing ~78% nitrogen and ~21% oxygen, with small amounts of argon, CO2, neon, etc., is the accurate description. The other options either swap the proportions or claim gases (like helium) that aren’t major components in the atmosphere.

The main idea is recognizing which two gases dominate Earth's atmosphere. Dry air is mostly nitrogen and oxygen, with nitrogen making up about 78% and oxygen about 21%. The rest—argon, carbon dioxide, neon and other trace gases—tresents only a small fraction. This makes nitrogen the most abundant gas and oxygen the second most abundant, which is why a statement listing ~78% nitrogen and ~21% oxygen, with small amounts of argon, CO2, neon, etc., is the accurate description. The other options either swap the proportions or claim gases (like helium) that aren’t major components in the atmosphere.