The second law of thermodynamics can be described by the following statements:
1. **The internal energy of the universe is constant (a):** This statement is not directly related to the second law of thermodynamics. It is more aligned with the first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed.
2. **Energy can be neither created nor destroyed (b):** This statement is also related to the first law of thermodynamics, not the second law. The first law focuses on the conservation of energy.
3. **When an isolated system undergoes a spontaneous change, the entropy of the system will increase (c):** This statement accurately describes the second law of thermodynamics. The second law states that in any natural thermodynamic process, the total entropy of the system and its surroundings tends to increase over time, approaching a maximum value.
In summary, the correct statement that best describes the second law of thermodynamics is (c). The second law is fundamentally about the increase in entropy in isolated systems undergoing spontaneous changes.