CCl4, or carbon tetrachloride, is a colorless, volatile liquid with a sweet smell. It is composed of one carbon atom and four chlorine atoms. Historically, it was widely used as a solvent and in the production of refrigerants, but its use has declined due to environmental and health concerns. CCl4 is classified as a hazardous substance because it can cause liver and kidney damage if inhaled or ingested. It is also a potent ozone-depleting chemical, which has led to its regulation under various environmental laws, including the Montreal Protocol.