The concentration of potassium is higher in red blood cells than in the surrounding blood plasma. This higher concentration is maintained by the process of

active transport

Explanation:

Active transport -

It refers to the movement of the molecules from a region of lower concentration towards a region of higher concentration via a membrane, is referred to as active transport.

The process of active transport need to have some cellular energy.

Hence,

The concentration of potassium is maintained in the red blood cells via the process of active transport.