The rate at which a solid, liquid, and gaseous object or substance spreads spontaneously across space at a single time is called the diffusion rate of that object. The diffusion rate depends on the mass and density of the object.
Why is the diffusion rate of gaseous substances higher?
The highest diffusion rate of gaseous molecules is due to the fact that the molecular force of attraction between the molecules of the gaseous matter is very low. Due to which the molecules are located far away from each other. As a result, the molecules spread around very easily. So the rate of diffusion of gaseous substances is the highest.