Answer:
d. The entropy of the system increases, because the disorder caused by the change in state from solid to liquid water causes more disorder than liquid water cooling causes order.
Explanation:
Entropy of a state may be defined as a natural process and spontaneous process. It is the measure of the disorder and randomness of the event.
In the context, when ice cubes are dropped in a cup of hot water which is insulated, the ice melts and the water temperature decreases. According to the principle of entropy increase, option A is wrong as the process in not a reversible process and option B is also wrong as it violates the principle of energy conservation. So option D is correct which shows the disorderness of the system.