Which gas is most abundant in the Earth's atmosphere?

Nitrogen is the most abundant gas in the Earth’s atmosphere, making up about 78% of the atmosphere by volume. This significant presence plays a critical role in various atmospheric processes and the overall functioning of ecosystems. Nitrogen is an inert gas at atmospheric temperatures and pressures, which means it does not readily react with other substances. This stability is essential for maintaining the balance of gases in the atmosphere and is also why nitrogen can dominate its composition without contributing directly to processes such as respiration, which primarily involve oxygen.

In contrast, oxygen, while essential for life and making up about 21% of the atmosphere, is significantly less abundant than nitrogen. Carbon dioxide is present in much smaller concentrations, approximately 0.04% by volume, although its impact on climate and life is profound. Argon, a noble gas, constitutes around 0.93% of the atmosphere and has minimal reactivity, but it is still far less abundant than nitrogen. Thus, the correct identification of nitrogen as the most prevalent gas in the atmosphere reflects its fundamental role in both the chemistry of the atmosphere and the broader environmental context.