Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A) : Large cold storage plants use ammonia as refrigerant, while domestic refrigerators use chlorofluorocarbons.
Reason (R) : Ammonia can be liquefied at ambient temperature and low pressure.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both (A) and (R) are true and (R) is the correct explanation of (A)
A refrigerator works by a refrigerant that is liquefied by compression and then allowed to evaporate: as the liquid turns back into vapour inside the cooling coils, it takes in heat from the space being cooled. A good refrigerant must therefore liquefy easily and take in a large amount of heat when it evaporates.
Assertion (A): Large cold storage plants use ammonia as refrigerant, while domestic refrigerators use chlorofluorocarbons. True. Ammonia is the standard refrigerant of large industrial cold stores, ice plants and dairies, while household refrigerators have used chlorofluorocarbons such as Freon-12.
Reason (R): Ammonia can be liquefied at ambient temperature and low pressure. True. Ammonia boils at about −33°C, so at room temperature a pressure of only about 8 to 10 atmospheres, easily given by a compressor, is enough to turn it into a liquid.
The Reason explains the Assertion: because ammonia liquefies so easily at ordinary temperatures, and absorbs a large amount of heat when it evaporates, it makes an efficient and cheap refrigerant for the big compressors of cold storage plants.