Which of the following best describes internal energy?

The correct answer is The total kinetic and potential energy of all particles in a system.

Definition lens: Give the precise definition, then add a context sentence that shows how it is used. This question asks: Which of the following best describes internal energy. The correct response is The total kinetic and potential energy of all particles in a system, because internal energy combines particle kinetic and potential energy. In Internal energy, the marking point should connect directly to describe how changing particle arrangement can change the potential energy of particles. 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 234 is distinct because it uses this exact question context and the definition lens rather than a generic particle-model sentence.