Which of the following is NOT considered a natural refrigerant?

The correct answer is that hydrochlorofluorocarbon (HCFC) is not considered a natural refrigerant. Natural refrigerants are defined as substances that naturally occur in the environment and have minimal impact on the ozone layer and global warming potential.

CO2, ammonia, and propane are all classified as natural refrigerants. CO2 (R-744) is a naturally occurring gas that is abundant in the Earth's atmosphere and has a low global warming potential when used as a refrigerant. Ammonia (R-717) is also a naturally occurring compound with properties that make it effective for refrigeration systems, particularly in industrial applications. Propane (R-290) is a hydrocarbon that is found in natural gas and is used in various applications due to its efficiency and environmental friendliness.

In contrast, HCFCs are synthetic compounds that were developed to replace chlorofluorocarbons (CFCs) in refrigeration and air conditioning systems but still contain chlorine, which contributes to ozone depletion. Therefore, HCFCs do not fit the classification of natural refrigerants.