Chlorine-35 is a stable isotope of the element chlorine, which has an atomic number of 17. It contains 18 neutrons in its nucleus, giving it a mass number of 35. Chlorine-35 is one of the two naturally occurring isotopes of chlorine, the other being Chlorine-37. This isotope is commonly found in nature, making up about 76% of all chlorine isotopes. Chlorine-35 plays a significant role in various chemical reactions and is used in applications such as water treatment and the production of chlorine gas. Its stable nature makes it important for scientific research and industrial processes.