What is the fraction of oxygen in air?
-
1/5
-
2/5
-
3/5
-
4/5
Reveal answer
Fill a bubble to check yourself
A
Correct answer
Explanation
Oxygen makes up approximately 21% of Earth's atmosphere by volume, which is roughly 1/5th. Nitrogen is the main component at about 78%, with trace gases making up the remaining 1%.
AI explanation
Air is roughly 21% oxygen by volume, which is closest to 1/5 (20%). The other fractions (2/5=40%, 3/5=60%, 4/5=80%) are far too high and would be lethal/unrealistic oxygen concentrations. Nitrogen is the majority gas (~78%, close to 4/5), which some students confuse with oxygen — but the question asks specifically about oxygen, so 1/5 is the standard approximate answer used in basic science/aptitude tests.