Bromine is a halogen element that is a reddish-brown liquid at room temperature. It is one of only two liquid elements at room temperature (the other is mercury). Bromine is highly reactive and can be dangerous if not handled properly. Its reactivity makes it useful in a variety of applications, including flame retardants for textiles and plastics, water purification, and in the production of pharmaceuticals. It is also used in photography, where it plays a key role in both developing and stopping the development of photographic film. Despite its usefulness, bromine can be harmful to the environment if released into the atmosphere or water supply.