What is the percentage of oxygen in the air? Name the biological process by which it is mainly returned to the atmosphere.

Oxygen:

1. It is a colorless, odorless reactive gas we inhale during respiration.
2. The percentage of oxygen in the air is 20.94%.
3. The biological process by which it is mainly returned to the atmosphere is photosynthesis.
4. This is the process by which green plants and other organisms prepare their food using sunlight.