Which statement 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.

Boundary lens: Keep this separate from nearby specification points that use similar words but test a different idea. This question asks: Which statement 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) State that pressure multiplied by volume is 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 538 is distinct because it uses this exact question context and the boundary lens rather than a generic particle-model sentence.