Why do gas particles collide with the walls of their container?

The correct answer is Due to their random motion.

Application lens: Apply the rule to the specific sample or situation instead of reciting a broad fact. This question asks: Why do gas particles collide with the walls of their container. The correct response is Due to their random motion, because gas pressure comes from particle collisions with container walls. In Particle motion in gases, the marking point should connect directly to use the particle model to explain why gas pressure changes when gas particles collide with container walls. 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 499 is distinct because it uses this exact question context and the application lens rather than a generic particle-model sentence.