Refer to figure.
Air is primarily composed of the following gases:

1. Nitrogen (N₂): Makes up approximately 78% of the atmosphere by volume. Nitrogen is a non-reactive gas essential for life and various industrial processes.
2. Oxygen (O₂): Constitutes about 21% of the atmosphere by volume. Oxygen is crucial for aerobic respiration in most organisms and combustion processes.
3. Argon (Ar): Makes up around 0.93% of the atmosphere. Argon is a noble gas that is chemically inert and fills space between other molecules.
4. Carbon Dioxide (CO₂): Represents about 0.04% of the atmosphere. Carbon dioxide plays a critical role in the Earth's carbon cycle, influencing climate and photosynthesis.
5. Trace Gases: These include water vapor (variable depending on location and weather), methane (CH₄), ozone (O₃), and other gases present in very small amounts. Despite their low concentrations, these gases can have significant impacts on climate and atmospheric processes.

This mixture of gases makes up Earth's atmosphere, which is vital for supporting life, regulating climate, and protecting the planet from harmful solar radiation.

NOTE:
The percentage of gases is constant with increasing altitude.