What process involves collecting platelets while returning whole blood elements to the donor?

The correct choice is apheresis. This process specifically involves the separation of blood components from a donor, allowing for the collection of a particular component, such as platelets, while the remaining components—such as red blood cells and plasma—are returned to the donor's circulation.

Apheresis can be utilized for various blood components, including platelets, leukocytes, and plasma, by utilizing a machine that separates blood into its components. This technique is advantageous because it enables the collection of a higher quantity of platelets than would be possible through traditional whole blood donation, benefiting patients who require platelet transfusions.

Plasma exchange, while similar in nature, specifically denotes the process of removing plasma and replacing it with a substitute solution, rather than focusing on the collection of platelets. Whole blood donation typically involves the collection of all components of blood without any separation or return of elements, and fractionation refers to the process of separating blood into its components after collection, rather than during donation. These key distinctions highlight why apheresis is the appropriate term for this process.