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

The correct answer is Pressure is inversely proportional to volume.

Method lens: First identify the measured quantity, then match the equation or particle idea to the command word. This question asks: What is the relationship between gas pressure and the volume of 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 use the particle model to explain why gas pressure changes when gas particles collide with container walls. 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 500 is distinct because it uses this exact question context and the method lens rather than a generic particle-model sentence.