What percentage of oxygen is typically found in the air?

The typical concentration of oxygen in the Earth's atmosphere is approximately 21%. This percentage is crucial for various biological and chemical processes, particularly for the respiration of aerobic organisms, including humans and animals.

Understanding this percentage is important for fields like environmental science, biology, and even industries related to combustion and fossil fuels, where oxygen levels can affect efficiency and safety. Monitoring oxygen levels is essential in various applications, including aviation, diving, and in creating environments for sensitive ecological or industrial processes.

The other choices reflect values that are not representative of the Earth's atmosphere. While they might seem close, they do not accurately capture the well-established figure of around 21% oxygen.