How does the mass of a diffusing molecule affect its rate of diffusion?

1. Molecules move constantly and randomly, at a rate that depends partly on their mass. 2. Heavier molecules move more slowly and therefore diffuse more slowly. 3. The reverse holds for lighter molecules, which move and diffuse faster. 4. Mass acts on every diffusing particle, charged or not, so restricting the effect to ions is wrong. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 5 "Structure and Function of Plasma Membranes", section 5.2 Passive Transport_