Here's why:

* Respiration is the process where living organisms take in oxygen and release carbon dioxide.

* Oxygen is a gas that is essential for cellular processes, such as energy production.

* Carbon dioxide is a waste product of these processes.

During respiration:

1. Inhalation: We breathe in air containing oxygen.

2. Oxygen Transport: Oxygen is transported throughout the body by red blood cells.

3. Cellular Respiration: Cells use oxygen to produce energy and release carbon dioxide as a byproduct.

4. Exhalation: Carbon dioxide is exhaled from the lungs, along with other gases like nitrogen.

So, the air we breathe in contains oxygen, and the air we breathe out contains carbon dioxide, which are both gases.