The Proportion of the Air We Breathe Accounted for by Oxygen

Question

The proportion of the air we breathe accounted for by oxygen is approximately
A)21%.
B)1%.
C)5%.
D)50%.
E)78%.

Accepted Answer

The correct proportion of oxygen in the air we breathe is approximately 21%. This is also known as the oxygen concentration in air and is sometimes denoted as O2%. The remaining components of air include nitrogen (approximately 78%), argon (approximately 0.93%), and trace amounts of carbon dioxide, neon, helium, methane, krypton, hydrogen, and xenon.