What percentage of air is made up of oxygen?

Oxygen makes up approximately 21% of the Earth's atmosphere. This composition is essential for life as we know it, as oxygen is crucial for the process of respiration in animals and humans, as well as for combustion processes. Understanding the percentage of oxygen in the atmosphere is important for various fields, including environmental science, chemistry, and even the operation of combustion appliances in the oilheat industry.

While other gases such as nitrogen (which constitutes about 78% of the atmosphere) and trace gases are present in varying amounts, the significant percentage of oxygen contributes to breathable air and is a vital component for many chemical reactions. This knowledge could be relevant in combustion efficiency and safety measures when dealing with heating systems that rely on combustion processes.