What is the main reason that mass is conserved during a change of state (Changes of state)

The correct answer is Particles are rearranged but not created or destroyed..

Comparison lens: State both sides of the comparison so the contrast is explicit rather than implied. This question asks: What is the main reason that mass is conserved during a change of state (Changes of state). The correct response is Particles are rearranged but not created or destroyed., because gas pressure comes from particle collisions with container walls. In Changes of state, the marking point should connect directly to use the particle model to explain why gases are less dense than solids or liquids. 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 197 is distinct because it uses this exact question context and the comparison lens rather than a generic particle-model sentence.