Diffusion rate of gases
Temperature is directly proportional to diffusion rate.

Diffusion, being the dispersion of molecules throughout a space, is affected by the speed of molecules and the density of the space through which the molecules are being dispersed.  

An increase in temperature increases the speed at which molecules move at. This is because the average kinetic energy of the gas molecules is proportional to the absolute temperature of the gas. Increased speed will yield faster and more even diffusion.    

Average Kinetic Energy of gas molecules = $\frac{3}{2}RT$. 

Therefore, decrease in temperature will cause molecules to slow down (due to reduction in average kinetic energy). Hence rate of diffusion decreases.

I hope this helps!