Final answer:
Diffusion of a gas is more rapid when the partial pressure gradient is large because it indicates a greater difference in concentration between two areas.
Step-by-step explanation:
Diffusion of a gas occurs more quickly if the partial pressure gradient is large. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. In the context of gases, the partial pressure of a gas in a mixture represents its concentration. According to Dalton's law, each gas in a mixture exerts its own pressure independent of other gases, and according to Henry's law, the amount of gas that dissolves in a liquid is proportional to its partial pressure. A large partial pressure gradient means there is a big difference in the concentration of the gas between two regions, such as between the alveoli and the blood in the lungs, which results in a more rapid rate of diffusion.