Final answer:
The mass of a gas molecule affects its diffusion speed, with heavier molecules diffusing more slowly than lighter ones. Temperature and density also influence diffusion, while greater travel distance slows it down.
Step-by-step explanation:
The property of a gas molecule that affects the speed at which it diffuses is its mass.
The heavier molecules move more slowly and, as a result, diffuse more slowly than lighter molecules.
This is because at a given temperature, the average molecular speed is inversely proportional to the molecular mass.
Additionally, the diffusion constant increases with temperature, signifying that average molecular speed, and thus diffusion rate, increase as the temperature rises.
Lastly, solution density and the distance that molecules must travel also affect diffusion, with density being inversely proportional to molecular movement and greater distance slowing down the diffusion.