What designation do fluorinated refrigerants that start with a number 5 have?

Fluorinated refrigerants that start with a number 5 are designated as azeotropic. Azeotropic mixtures are characterized by a constant boiling point and do not change composition during phase changes, which makes them behave like a single substance under certain conditions. This is essential in refrigeration applications, as it allows for more stable and predictable performance during the refrigeration cycle.

In reference to the other options, azeotropic is distinct from zeotropic mixtures, which do not have a constant boiling point and can have varying compositions during phase changes. Hydrochlorofluorocarbons and chlorofluorocarbons refer to specific categories of refrigerants that are not defined by numerical designations but rather by their chemical composition and environmental impact. Therefore, the classification of refrigerants starting with a number 5 as azeotropic is based on their physical properties and performance characteristics in refrigeration systems.