The second law of thermodynamics states that in every spontaneous process, the entropy of the universe

• A. decreases
• B. remains constant
• C. fluctuates
• D. increases

Answer: (D)

The essential idea is that spontaneous processes drive energy to spread out and become more accessible in more ways. Entropy measures how many microscopic configurations are possible for a given state. When a process happens on its own, the system and its surroundings tend to move toward more probable arrangements, so the total number of possible configurations increases. That means the entropy of the universe (the system plus surroundings) increases for spontaneous changes. If a process were perfectly reversible, the total entropy would stay the same; if a process reduced entropy, it wouldn’t be spontaneous unless external work or constraints were used to impose order elsewhere. A classic example is a gas expanding freely into a vacuum—the gas disperses, creating many more microstates and raising the universe’s entropy. So, the correct statement is that the entropy of the universe increases.