Chlorine

Chlorine (Cl2) is among the ten highest volume chemicals manufactured in the United States. It is produced commercially by electrolysis of sodium chloride brine. Chlorine is used in industry and in household cleaning products. Chlorine was also the first poison gas to be used as a weapon during World War I.
Some of the chemical/physical properties of chlorine include:
Chlorine is a yellow-green gas at room temperature.
Chlorine has a pungent, irritating odor similar to bleach that is detectable at low concentrations.
The density of chlorine gas is approximately 2.5 times greater than air, which will cause it to initially remain near the ground in areas with little air movement.
Chlorine is not flammable, but may react explosively or form explosive compounds with many common substances (including acetylene, ether, turpentine, ammonia, natural gas, hydrogen, and finely divided metals).
Chlorine is slightly water soluble, and reacts with moisture to form hypochlorous acid (HClO) and hydrochloric acid (HCl).
Chlorine is commonly pressurized and cooled for storage and shipment as an amber-colored liquid.