RAS question
Which gas is most abundant in the Earth's atmosphere?
Correct answer: (C) Nitrogen.
Nitrogen is the most abundant gas in Earth's atmosphere, making up about 78% of the air near the surface.
Explanation
Nitrogen is the right answer because it forms the clear majority of Earth's atmosphere by volume. Nitrogen is approximately 78.09%, ahead of oxygen at 20.95%, argon at 0.93%, and carbon dioxide at about 0.04%. NASA Science: Facts About Earth states the same basic composition near the surface: 78% nitrogen, 21% oxygen, and 1% other gases such as argon, carbon dioxide, and neon. That ranking is the key point for the MCQ: oxygen is vital for respiration, but it is not the largest atmospheric component. Nitrogen also matters beyond memorisation because it links to the nitrogen cycle and plant growth, making it a basic science-and-environment fact.
Why the other options are wrong
- (A) Oxygen is second in abundance, at about 21% of the atmosphere, so it is important but not the largest component.
- (B) Carbon dioxide is only about 0.04% of the atmosphere, far below nitrogen and oxygen by volume.
- (D) Argon accounts for about 0.93% of the atmosphere, placing it among the minor gases rather than the most abundant one.
Concept
This tests the basic composition of Earth's atmosphere, a recurring RAS science topic because it links static general science with environment questions such as the nitrogen cycle and plant growth.