What happens to the density of a substance when it is heated and expands (Density of materials)

The correct answer is Density decreases.

Exam lens: Write the relationship, substitute values only when needed, and finish by interpreting the result. This question asks: What happens to the density of a substance when it is heated and expands (Density of materials). The correct response is Density decreases, 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 59 is distinct because it uses this exact question context and the exam lens rather than a generic particle-model sentence.