What happens to the pressure of a gas when its volume decreases at constant temperature?

The correct answer is The pressure increases.

Cause lens: Name the cause, then state the effect on particles, pressure, density, or energy. This question asks: What happens to the pressure of a gas when its volume decreases at constant temperature. The correct response is The pressure increases, 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 520 is distinct because it uses this exact question context and the cause lens rather than a generic particle-model sentence.