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

The most abundant gas in the Earth's atmosphere is nitrogen, which comprises about 78% of the atmosphere by volume. This high concentration plays a crucial role in the overall composition and stability of the atmosphere. Nitrogen is relatively inert, which means it does not easily react with other substances, thereby contributing to the consistent climate and atmospheric pressure that support life on Earth.

In contrast, oxygen, while essential for aerobic respiration in many organisms, makes up around 21% of the atmosphere. Carbon dioxide is present in much smaller quantities, approximately 0.04%, and is significant primarily for its role in photosynthesis and as a greenhouse gas. Argon, a noble gas, is even less abundant, constituting about 0.93% of the atmosphere. Thus, nitrogen's dominance in terms of percentage makes it the most abundant gas in the atmosphere.