What percentage of the air is oxygen?

The choice indicating that 21% of the air is oxygen is accurate based on the composition of Earth's atmosphere. In the atmosphere, nitrogen makes up approximately 78%, oxygen about 21%, and the remaining 1% includes argon, carbon dioxide, and other gases in trace amounts. This specific percentage is significant because it highlights the balance necessary for life on Earth, as oxygen is vital for respiration in most living organisms. Understanding the role of oxygen in the atmosphere is crucial for a variety of applications, including agritechnology, where the growth and health of plants depend on adequate oxygen levels in the soil and air. The misconception about the percentage can often arise from oversimplifications or misinterpretations of atmospheric science, but the widely accepted figure is indeed 21%.