Entropy is defined as:

• A. Randomness or disorder in a system
• B. Energy efficiency
• C. Rate of change
• D. Useful work

Answer: (A)

Entropy is a measure of randomness or disorder in a system. In thermodynamics, it reflects how energy is spread among all possible microstates; higher entropy means the system is more disordered and energy is less available to do work. This idea aligns with the tendency of isolated systems to move toward greater disorder over time, as described by the Second Law. The other options don’t capture what entropy represents: energy efficiency refers to how effectively energy is converted to useful work, not to disorder; rate of change is about speed or velocity of change, not the level of disorder; useful work is about the portion of energy that can perform work, which is related to entropy but is not the definition itself.