What happens to the particles in a substance when it melts?

The correct answer is Particles gain energy and move further apart..

Definition lens: Give the precise definition, then add a context sentence that shows how it is used. This question asks: What happens to the particles in a substance when it melts. The correct response is Particles gain energy and move further apart., because gas pressure comes from particle collisions with container walls. In Changes of state, the marking point should connect directly to describe solids, liquids and gases in terms of particle arrangement and movement. 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 Changes of state and the particle model, 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 114 is distinct because it uses this exact question context and the definition lens rather than a generic particle-model sentence.