Final answer:
The entropy of an isolated system always increases during a spontaneous change reflecting the second law of thermodynamics which states that entropy must increase or remain constant in such processes.
Step-by-step explanation:
What happens to the entropy of an isolated system in the course of a spontaneous change? The correct answer is (d) the entropy of the system increases. According to the second law of thermodynamics, the total entropy of an isolated system not in thermal equilibrium will always increase.
Spontaneous processes in such a system result in increased entropy due to the dispersion of energy from a concentrated to a more dispersed state. Therefore whenever a spontaneous change occurs in an isolated system, the system moves towards a state of higher disorder and randomness which equates to an increase in entropy. This is a fundamental concept in thermodynamics which states that the total entropy of a system either increases or remains constant; it never decreases.