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

The correct answer is Pressure is inversely proportional to volume.

Evidence lens: Use the data, graph feature, practical observation, or particle behaviour that proves the answer. This question asks: What is the relationship between pressure and volume for a fixed mass of gas at constant temperature (Pressure in gases (physics only)). The correct response is Pressure is inversely proportional to volume, 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) Explain how changing the volume of a fixed mass of gas changes the frequency of particle collisions 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 513 is distinct because it uses this exact question context and the evidence lens rather than a generic particle-model sentence.