Which of the following is NOT an HFC refrigerant?

R-12 is recognized as a chlorofluorocarbon (CFC) and not an HFC (hydrofluorocarbon). CFCs like R-12 were commonly used in refrigeration and air conditioning systems but have been phased out due to their significant ozone depletion potential.

In contrast, HFCs were developed as alternatives to CFCs and do not contain chlorine, which is responsible for ozone layer damage. While options such as R-143a, R-23, and R-124 are classified as HFCs or have similar properties, R-12 distinctly represents an older category of refrigerants known for their adverse environmental impact, specifically concerning ozone depletion. Thus, identifying R-12 as not belonging to the HFC category is accurate.