Explain the relationship between pressure and volume for a fixed mass of gas at constant temperature.

For a fixed mass of gas at constant temperature, the pressure of the gas is inversely proportional to its volume. This means that if the volume decreases, the pressure increases, and vice versa, as described by the equation pressure x volume = constant.

Cause lens: Name the cause, then state the effect on particles, pressure, density, or energy. This question asks: Explain the relationship between pressure and volume for a fixed mass of gas at constant temperature. The correct response is For a fixed mass of gas at constant temperature, the pressure of the gas is inversely proportional to its volume. This means that if the volume decreases, the pressure increases, and vice versa, as described by the equation pressure x volume = 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 544 is distinct because it uses this exact question context and the cause lens rather than a generic particle-model sentence.