Which principle states energy cannot be created or destroyed?

• A. Law of Conservation of Energy
• B. Law of Conservation of Mass
• C. Law of Entropy
• D. Law of Thermodynamics

Answer: (A)

Energy conservation is the main idea here: energy cannot be created or destroyed, only changed from one form to another or moved between objects. This is captured by the Law of Conservation of Energy, often called the first law of thermodynamics. In a closed system, the total energy before a process equals the total energy after. For example, a pendulum continually swaps potential energy for kinetic energy, yet the sum remains constant. A lamp converts electrical energy into light and heat, still conserving total energy. In chemical reactions, chemical energy may become kinetic or thermal energy, but the overall energy balance stays the same.

The other ideas don’t capture this universal accounting. Conservation of mass concerns matter, not energy. Entropy describes the tendency toward greater disorder and the dispersal of energy, not the bookkeeping of energy itself. The law of thermodynamics is a broad set of principles, and the specific statement that energy cannot be created or destroyed is the particular first law within that broad framework.