What is the relationship between pressure and volume for a fixed mass of gas at constant temperature (Particle motion in gases)

The correct answer is Pressure is inversely proportional to volume.

Comparison lens: State both sides of the comparison so the contrast is explicit rather than implied. This question asks: What is the relationship between pressure and volume for a fixed mass of gas at constant temperature (Particle motion in gases). The correct response is Pressure is inversely proportional to volume, because gas pressure comes from particle collisions with container walls. In Particle motion in gases, the marking point should connect directly to explain that the force from particle collisions produces gas pressure. 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 473 is distinct because it uses this exact question context and the comparison lens rather than a generic particle-model sentence.