During a change of state, why does the temperature remain constant?

The correct answer is Energy is used to change the potential energy of particles.

Application lens: Apply the rule to the specific sample or situation instead of reciting a broad fact. This question asks: During a change of state, why does the temperature remain constant. The correct response is Energy is used to change the potential energy of particles, because the particle model explains the observable property using particles. In Changes of state and specific latent heat, the marking point should connect directly to apply MS 4a and MS 4c skills when interpreting graphs of temperature against time. 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 439 is distinct because it uses this exact question context and the application lens rather than a generic particle-model sentence.