When placed outside and exposed to the atmosphere, an ice cube melts, forming a thin film of liquid on the ground. Overnight, the liquid freezes, returning to the initial temperature of the ice cube. The water making up the cube undergoes (a) a thermodynamic cycle, (b) a reversible process, (c) an irreversible process, (d) none of the above.

Option A and C are correct.

Explanation:

First of all, a thermodynamic circle is closed and gotten when our starting and ending points are the same. Now, from the question, we can see that the water starts and ends on the same temperature and pressure. Thus, we can say that a thermodynamic circle has occurred. So, option A is correct.

Now, to achieve a reversible process, there should be no exergy losses could cause rise in exergy entropy. There are two possible causes which we cannot eliminate as both are useful. First is exergy friction while the second cause is heat exchange at different temperatures of heat reservoirs and our cube. This second cause is confirmed because our cube while melting is on lower temperature than it's surrounding. This causes rise in entropy in overall system, thus making the process irreversible. So option C is correct.