Which factor decreases the diffusion of a solute through a solution?

The size of a molecule is a significant factor affecting its ability to diffuse through a solution. As the size of the molecule increases, the diffusion process becomes less efficient due to several reasons, including increased resistance to movement in the solvent and a larger mass that needs to be moved through the medium. Larger molecules generally experience more friction as they interact with the surrounding solvent molecules, which can impede their movement.

In contrast, other factors mentioned contribute to increased diffusion rates. An increased concentration gradient provides a steeper difference in solute concentration, enhancing the driving force for diffusion. A higher diffusion coefficient reflects a greater ability of molecules to move through the solvent, and a larger diffusion area allows more space for solute particles to move and spread out. Thus, while the other factors enhance diffusion, the increased size of the molecule acts to decrease its rate of diffusion through a solution.