What is the primary reason that gases are less dense than solids or liquids (Density of materials)

The correct answer is Particles in gases are more spread out.

Evidence lens: Use the data, graph feature, practical observation, or particle behaviour that proves the answer. This question asks: What is the primary reason that gases are less dense than solids or liquids (Density of materials). The correct response is Particles in gases are more spread out, because density links mass and volume, so the answer must preserve which quantity is being calculated. In Density of materials, the marking point should connect directly to describe how to determine the volume of an irregular solid using displacement of water. 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 81 is distinct because it uses this exact question context and the evidence lens rather than a generic particle-model sentence.