Define density and provide the equation used to calculate it.

Density is defined as mass per unit volume. The equation for density is density = mass / volume.

Evidence lens: Use the data, graph feature, practical observation, or particle behaviour that proves the answer. This question asks: Define density and provide the equation used to calculate it. The correct response is Density is defined as mass per unit volume. The equation for density is density = mass / volume., 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 apply AT 1 and AT 3 skills when measuring mass and volume. 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 93 is distinct because it uses this exact question context and the evidence lens rather than a generic particle-model sentence.