Please circle the process which does not involve irreversibility: (A) The conversion of mechanical work to heat by friction. (B) Conversion of electrical energy to thermal energy through a resistor heater. (C) Mixing of O2 and N2 for the production of air. (D) The theoretical conversion from electricity to mechanical work.

Mixing of O2 and N2 for the production of air.

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

water is used to store them because it would keep the radiation from getting out in the open and causing harm to the workers

i just learnt this recently but i need to look through my notes again