Chlorine is a chemical element with the symbol Cl and atomic number 17. It is a halogen, which means it is a highly reactive non-metal. Chlorine is a GAS at room temperature and pressure, and it has a characteristic pungent odor. Chlorine is used in many industrial processes, such as water treatment, bleaching, and disinfection. It is also used in the production of plastics, pharmaceuticals, and other products. Chlorine is essential for life on Earth, as it helps to maintain the balance of oxygen and nitrogen in the atmosphere.