Explain why decreasing the volume of a gas at constant temperature increases its pressure.

Decreasing the volume of a gas at constant temperature leads to more frequent collisions of gas particles with the walls of the container. This increase in collision frequency results in a greater force exerted on the walls, which raises the pressure of the gas.

Comparison lens: State both sides of the comparison so the contrast is explicit rather than implied. This question asks: Explain why decreasing the volume of a gas at constant temperature increases its pressure. The correct response is Decreasing the volume of a gas at constant temperature leads to more frequent collisions of gas particles with the walls of the container. This increase in collision frequency results in a greater force exerted on the walls, which raises the pressure of the gas., 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 why decreasing the volume of a gas at constant temperature increases its pressure. 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 521 is distinct because it uses this exact question context and the comparison lens rather than a generic particle-model sentence.