Describe how the particle arrangement changes when a solid melts into a liquid.

When a solid melts, its particles move from a closely packed, fixed arrangement to a more loosely arranged state. The particles in the liquid are still in contact but can move past each other, allowing the liquid to flow.

Comparison lens: State both sides of the comparison so the contrast is explicit rather than implied. This question asks: Describe how the particle arrangement changes when a solid melts into a liquid. The correct response is When a solid melts, its particles move from a closely packed, fixed arrangement to a more loosely arranged state. The particles in the liquid are still in contact but can move past each other, allowing the liquid to flow., because changes of state are explained by particle energy and arrangement. In Changes of state, the marking point should connect directly to explain melting using increased particle energy and changed particle arrangement. 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 125 is distinct because it uses this exact question context and the comparison lens rather than a generic particle-model sentence.