Which of the following best describes internal energy?

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

Boundary lens: Keep this separate from nearby specification points that use similar words but test a different idea. 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 changes of state are explained by particle energy and arrangement. In Internal energy, the marking point should connect directly to explain why energy transfer can change temperature without changing state. 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 250 is distinct because it uses this exact question context and the boundary lens rather than a generic particle-model sentence.