Chlorine does not naturally occur uncombined. Commercial production of chlorine is done via the electrolysis of sodium chloride brine.
Chlorine has multiple uses; it is used to disinfect swimming pools and to sterilize drinking water. It is also used to manufacture several commonly used products like plastic, paints, medicines, textiles and paper.
Chlorine is the 21st most abundant element on Earth, and it is the second most common halogen. In its natural gas state, chlorine is harmful to human health. It was the first gas to be used as a weapon during World War I. Its health effects are largely caused by it corrosive properties.