Cl, or chlorine, is a chemical element with the symbol Cl and atomic number 17. It is a yellow-green gas at room temperature and is part of the halogen group in the periodic table. Chlorine is highly reactive and is commonly used in disinfectants, bleach, and water treatment to kill bacteria and other pathogens. In nature, chlorine is found primarily in the form of sodium chloride, or table salt, which is abundant in seawater. It plays a crucial role in various industrial processes, including the production of plastics like polyvinyl chloride (PVC) and in the manufacture of pesticides and other chemicals.