Which unit is used to express density in the metric system?

The correct answer is kilograms per cubic meter.

Evidence lens: Use the data, graph feature, practical observation, or particle behaviour that proves the answer. This question asks: Which unit is used to express density in the metric system. The correct response is kilograms per cubic meter, because the particle model explains the observable property using particles. In Density of materials, the marking point should connect directly to required practical activity 5: use appropriate apparatus to determine densities of irregular solid objects. 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 57 is distinct because it uses this exact question context and the evidence lens rather than a generic particle-model sentence.