Which of the following statements correctly describes 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 multiplied by volume is constant.

Definition lens: Give the precise definition, then add a context sentence that shows how it is used. This question asks: Which of the following statements correctly describes 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 multiplied by volume is constant, 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) Apply the relationship pressure x volume = constant 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 546 is distinct because it uses this exact question context and the definition lens rather than a generic particle-model sentence.