Nitrogen is the most abundant gas in the Earth’s atmosphere, comprising about 78% of the atmosphere by volume. It is a colorless, odorless gas crucial for various biological and chemical processes. While nitrogen itself is inert and does not readily react with other substances, it is a vital component of amino acids, proteins, and nucleic acids found in living organisms. The nitrogen cycle is essential for providing usable nitrogen to ecosystems through processes like fixation by bacteria, allowing plants to absorb it and incorporate it into biological systems.