R-12, also known as dichlorodifluoromethane, is a type of refrigerant that was widely used in air conditioning and refrigeration systems. It is a colorless gas with a sweet odor and was popular due to its efficiency in heat transfer and low toxicity. However, R-12 is a chlorofluorocarbon (CFC), which contributes to ozone layer depletion. Due to environmental concerns, the production of R-12 was phased out under the Montreal Protocol in the 1990s. Alternatives, such as R-134a and R-410A, have since been developed to replace R-12 in various applications, helping to reduce the impact on the ozone layer.