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

The most common gas in Earth’s atmosphere is nitrogen, making up about 78% of the air by volume. Oxygen comes second, comprising approximately 21%, with the remaining 1% consisting of trace gases, including argon, carbon dioxide, and others. Nitrogen is largely inert, meaning it doesn’t react easily with other elements, which makes it stable in the atmosphere. It plays a key role in the nitrogen cycle, which is essential for the growth of plants and the functioning of ecosystems.