Answer:
Mixing of O2 and N2 for the production of air.
Step-by-step explanation:
An irreversible process is defined as any process which cannot return both the system and its surroundings to their original conditions. That is, the system and its surroundings would not return to their original conditions if the process was reversed. Irreversible Processes usually increase the entropy of the universe.
Processes that involve evolution of heat are usually irreversible processes since heat is lost to the surrounding. Hence the answer