Assertion (A) : Large cold storage plants use ammonia as refrigerant while domestic refrigerators use chlorofluorocarbons. Reason (R) : Ammonia can be liquified at ambient temperatures at low pressures.

The assertion is correct: industrial and large cold‑storage systems commonly use ammonia (R‑717) because of its high efficiency and long history of industrial use, while CFCs were widely used in domestic refrigerators historically due to their non‑toxicity and stability [1]. The reason given is incorrect. Anhydrous ammonia has a normal boiling point near −33°C, so to keep it as a liquid at typical ambient temperatures it must be stored at elevated pressures; ammonia refrigeration systems therefore store and handle ammonia under pressure and exploit its vaporization at low temperatures for cooling—contradicting the claim that it liquefies at ambient temperature at low pressures.

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 6: Environmental Degradation and Management > ozone depletion > p. 12