When gas particles collide with the walls of their container, what do they exert?

The correct answer is A force.

Evidence lens: Use the data, graph feature, practical observation, or particle behaviour that proves the answer. This question asks: When gas particles collide with the walls of their container, what do they exert. The correct response is A force, because density links mass and volume, so the answer must preserve which quantity is being calculated. In Pressure in gases (physics only), the marking point should connect directly to (Physics only) Interpret pressure-volume data for a fixed mass of gas at constant temperature. 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 Particle model and pressure, 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 573 is distinct because it uses this exact question context and the evidence lens rather than a generic particle-model sentence.