Final answer:
The desirable property of ammonia refrigerant oil is being free of water. This is important to prevent issues such as ice formation in refrigeration systems, which can lead to reduced efficiency and potential safety hazards.
Step-by-step explanation:
The desirable property of ammonia refrigerant oil is being free of water (B). Ammonia refrigerant oil is crucial for the effective functioning of refrigeration systems that use ammonia as a refrigerant. A high paraffin content is generally not desirable in refrigerant oils because it can lead to the formation of wax and other deposits. A very low flashpoint is not desirable, as it can be a safety hazard.
Water in the refrigerant oil can cause multiple issues, such as ice formation at low temperatures, which can clog the expansion valves and reduce efficiency. Therefore, ensuring that refrigerant oil is free of water is critical for maintaining the performance and safety of the ammonia refrigeration system.