# Question #6c305

${F}_{2}$ being lightest, diffuses fastest. $C {l}_{2}$, being heaviest will diffuse most slowly.
Now, since KE is given by $\frac{1}{2} m {v}^{2}$, it follows that heavier molecules move more slowly on average (at equal temp.). This is the key to diffusion. Rate of diffusion is tied to the speed of the molecules. Faster moving molecules diffuse at a greater rate.