What is the formula for calculating density?

The correct answer is Density = mass / volume.

Particle lens: Describe arrangement, motion, spacing, collisions, or energy changes only when they are relevant here. This question asks: What is the formula for calculating density. The correct response is Density = mass / volume, because the particle model explains the observable property using particles. In Density of materials, the marking point should connect directly to compare densities of materials using calculated or measured values. 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 108 is distinct because it uses this exact question context and the particle lens rather than a generic particle-model sentence.