What is defined as the total kinetic energy and potential energy of all particles in a system?

The correct answer is Internal energy.

Boundary lens: Keep this separate from nearby specification points that use similar words but test a different idea. This question asks: What is defined as the total kinetic energy and potential energy of all particles in a system. The correct response is Internal energy, because internal energy combines particle kinetic and potential energy. In Internal energy, the marking point should connect directly to define internal energy as the total kinetic energy and potential energy of all particles in a system. If the question includes values, the working must keep the appropriate unit and operation; if it is an explanation, it must name the relevant particle behaviour or energy change. This item belongs to Internal energy and energy transfers, so avoid answers that switch to a different quantity, confuse heat with temperature, or describe gas pressure without collisions when collisions are the reason. Checkpoint 214 is distinct because it uses this exact question context and the boundary lens rather than a generic particle-model sentence.