Final answer:
option b.When heated, R-12 changes to phosgene (Option B). R-12 is a CFC that decomposes at high temperatures, potentially forming toxic gases such as phosgene.
Step-by-step explanation:
When heated, R-12, which is also known as Freon-12 (CCl2F2), changes to phosgene (B). Freon-12 is a chlorofluorocarbon (CFC) that was commonly used as a refrigerant and propellant before it was banned due to its harmful effects on the ozone layer.
The breakdown of CFCs like R-12 can occur at high temperatures or when exposed to ultraviolet light, leading to the release of chlorine atoms, which can catalyze the destruction of ozone. Specifically, when R-12 is exposed to high temperatures, such as in the presence of a fire, it decomposes and can form phosgene, which is a toxic gas (Cl2CO). Carbon tetrachloride (CCl4) was historically used in the production of R-12.