Which of the following is considered a refrigerant?

Freon is considered a refrigerant because it was specifically designed for use in cooling systems and has the properties necessary for phase change during the refrigeration cycle. Refrigerants are substances that absorb heat at a low temperature and release it at a higher temperature, allowing for effective heat exchange in cooling applications. Freon, a brand name for a class of chemicals known as chlorofluorocarbons (CFCs), has a low boiling point and is effective in transferring heat, making it widely used in air conditioning and refrigeration systems.

Water, while it can be used in some cooling applications, does not fit the standard definition of a refrigerant used in vapor-compression refrigeration. Air, although it does have cooling properties, does not function as a refrigerant in the same sense, as it is not capable of undergoing a phase change in the refrigeration process. Ozone, on the other hand, is not used as a refrigerant; instead, it is often associated with environmental issues related to stratospheric ozone depletion. Thus, Freon stands out as the proper choice among the options provided for its specific application as a refrigerant.