What is the largest percentage of the air we breathe composed of?

The composition of the air we breathe is primarily made up of nitrogen, which accounts for about 78% of the Earth's atmosphere. This significant proportion makes nitrogen the largest component of the air. While oxygen is the second most abundant gas at about 21%, other gases like carbon dioxide and argon are present in much smaller amounts, with carbon dioxide typically around 0.04% and argon about 0.93%. Understanding this composition is important in fields such as exercise physiology, as it impacts respiration and oxygen delivery during physical activity.