One type of cloud is a nimbostratus which is

Nimbostratus clouds are really dark and thick, "featurless" lowlaying clouds. They usually block out any sunlight.

answer: the rate of diffusion increases with increase in temperature.

increase in temperature, increases the molecular/particles speed (kinetic energy. diffusion means movement of particles through the material.

generally, the heavier the particle the more it interacts with the environment and more the temperature matters. so higher temperature results in higher diffusion.