Common refrigerants include which of the following?

The correct response encompasses all of the listed options because each one is a recognized refrigerant utilized in various cooling systems.

Freon, particularly a class of compounds known as chlorofluorocarbons (CFCs), has been widely used in refrigeration and air conditioning systems. It is notable for its effectiveness in heat transfer and stability, but concerns over its environmental impact, particularly ozone depletion, have led to its phasedown in many countries.

Ammonia has a long history as a refrigerant due to its high efficiency and low cost, particularly in commercial refrigeration applications. It is a natural refrigerant that poses lower risks of contributing to global warming than synthetic options, but it is toxic and requires careful handling.

Carbon dioxide is becoming increasingly popular as a refrigerant, especially in low-temperature applications and in supermarket refrigeration systems. It has a low global warming potential and is environmentally friendly, but it operates at much higher pressures than traditional refrigerants, necessitating specialized equipment.

Each of these refrigerants, whether synthetic or natural, plays an important role in different refrigeration systems. Their presence in the list underscores the diversity of refrigerant options available in the industry, making the choice of "all of the above" the correct answer.