Describe how the particle arrangement and movement differ between solids, liquids, and gases.

In solids, particles are closely packed in a fixed arrangement and vibrate in place. In liquids, particles are still close but can move past each other, allowing liquids to flow. In gases, particles are far apart and move freely, filling the available space.

Boundary lens: Keep this separate from nearby specification points that use similar words but test a different idea. This question asks: Describe how the particle arrangement and movement differ between solids, liquids, and gases. The correct response is In solids, particles are closely packed in a fixed arrangement and vibrate in place. In liquids, particles are still close but can move past each other, allowing liquids to flow. In gases, particles are far apart and move freely, filling the available space., because density links mass and volume, so the answer must preserve which quantity is being calculated. In Changes of state, the marking point should connect directly to explain that mass is conserved when a substance changes 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 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 178 is distinct because it uses this exact question context and the boundary lens rather than a generic particle-model sentence.