15 N, or nitrogen-15, is a stable isotope of the element nitrogen. It has a nucleus containing seven protons and eight neutrons, making it heavier than the more common nitrogen-14 isotope. Nitrogen-15 is naturally occurring and constitutes about 0.36% of all nitrogen found in the environment. This isotope is often used in scientific research, particularly in agriculture and biochemistry. By tracing nitrogen-15 in plants and animals, researchers can study nitrogen cycles and understand how organisms utilize nitrogen in their growth and metabolism.