Which process describes the separation of substances in solution by their rates of diffusion through a semipermeable membrane?

The process that describes the separation of substances in solution by their rates of diffusion through a semipermeable membrane is dialysis. This process specifically involves moving solvent and solute molecules from an area of higher concentration to an area of lower concentration across a membrane that only allows certain molecules to pass through, effectively separating substances based on their size or molecular weight.

In a practical context, dialysis is commonly used in medical treatments, such as in kidney failure, where it helps remove waste products from the blood by exploiting the diffusion of smaller waste molecules while retaining larger blood components.

To understand why this option is correct, consider the nature of the semipermeable membrane used in dialysis, which selectively allows certain substances to diffuse while restricting others based on size. This distinguishes it from other processes where diffusion may be involved but does not specifically require a semipermeable membrane for the separation of substances.