Final answer:
As a system loses its ability to do useful work, its entropy increases. This is due to the Second Law of Thermodynamics which states that the entropy of an isolated system never decreases over time. Energy transfer from hot to cold also contributes to the increase in entropy.
Step-by-step explanation:
The issue at hand relates to the Second Law of Thermodynamics, which states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. Hence, as a system loses its ability to do useful work, the entropy of the system increases. Entropy, in this context, can be thought of as a measure of the randomness or disorder within a system. Therefore, the correct answer to the student's question is that C) entropy increases.
When looking at energy transfer, such as heat moving from a high to a low temperature, the entropy of the entire system increases. This is because energy spontaneously transfers from a more concentrated to a more dispersed state, further contributing to the increase in entropy. An example is when ice melts into water; the structured solid turns into a more disorderly liquid, thus increasing entropy.
Over time and on a universal scale, the increase in entropy means that the availability of energy to perform work is constantly decreasing. Eventually, when thermal equilibrium is reached, no work can be done. It's important to remember that while energy remains constant due to the First Law of Thermodynamics, its availability to do work decreases as entropy increases.