Which element constitutes the highest percentage by volume in air?

The element that constitutes the highest percentage by volume in air is nitrogen. In the Earth's atmosphere, nitrogen makes up about 78% of the total volume of air, making it the most abundant gas present. Its high abundance is a result of the natural processes that maintain the balance of gases in the atmosphere, as nitrogen is relatively stable and does not readily react with other elements under normal conditions.

Oxygen, while vital for many living organisms, accounts for approximately 21% of the atmosphere. Hydrogen is found in very small amounts, less than 1%, and carbon dioxide, although critically important in various environmental and biological processes, only constitutes about 0.04% of the atmosphere by volume. Understanding these proportions is crucial for fields related to environmental science, biology, and engineering, particularly when considering combustion, respiration, and atmospheric science.