What is the most abundant gas in Earth’s atmosphere?

The most abundant gas in Earth’s atmosphere is nitrogen, which makes up about 78% of the air by volume. Nitrogen is an inert gas, meaning it doesn’t readily react with other chemicals. It plays a critical role in the nitrogen cycle, helping to maintain soil fertility through processes like nitrogen fixation. The second most abundant gas is oxygen, which makes up about 21% of the atmosphere and is essential for respiration in most living organisms.