Which of the following is typically a refrigerant used in absorption refrigeration systems?

Ammonia is commonly used as a refrigerant in absorption refrigeration systems due to its thermodynamic properties and efficiency in this type of system. Absorption refrigeration relies on the principle of cooling through the absorption of refrigerant vapor by a secondary fluid, often an absorbent that allows for the refrigerant to be recycled and reused in the system.

Ammonia stands out because of its high efficiency and effectiveness at transferring heat, making it suitable for a variety of applications, especially in industrial and commercial refrigeration. It also has a relatively low environmental impact compared to some synthetic refrigerants.

In contrast, options like Freon are primarily associated with vapor-compression refrigeration systems rather than absorption systems. Carbon dioxide, while being used in certain refrigeration applications, is typically not the refrigerant of choice for absorption systems. Propane, although usable as a refrigerant, is more common in specific applications and does not have the same level of use in absorption refrigeration as ammonia does. Thus, due to its suitability and properties, ammonia is the correct refrigerant for absorption refrigeration systems.