What percentage of air consists of oxygen?

The correct answer is 21% because the composition of Earth's atmosphere is primarily made up of nitrogen (about 78%) and oxygen (approximately 21%). This percentage has been consistently measured and is foundational to our understanding of atmospheric chemistry and the respiratory needs of living organisms. The remainder of the atmosphere consists of trace gases, including argon, carbon dioxide, and others, which have minimal concentration but play crucial roles in various ecological and biological processes.

Understanding these percentages is essential in fields like agricultural biotechnology, as oxygen availability affects plant growth and photosynthesis, influencing agricultural productivity and biotechnological applications.