What is the unit of density?

The correct answer is kilograms per metre cubed.

Graph lens: Read the trend, flat section, gradient, or axis labels before explaining the physical meaning. This question asks: What is the unit of density. The correct response is kilograms per metre cubed, 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 identify density in kilograms per metre cubed or grams per centimetre cubed, mass in kilograms or grams and volume in metres cubed or centimetres cubed. 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 15 is distinct because it uses this exact question context and the graph lens rather than a generic particle-model sentence.