Final answer:
Potassium (K+) is the most prevalent cation inside cells, maintained by sodium-potassium pumps that utilize ATP for energy.
Step-by-step explanation:
The cation that is most prevalent inside cells is potassium (K+). This is due to the action of the sodium-potassium pumps located in the cell membranes, which actively transport sodium ions out of the cell while moving potassium ions in. These pumps are powered by ATP (adenosine triphosphate), the energy currency of the cell. As a result, the normal potassium concentration is roughly 30 times higher inside cells than outside, which is key for various cellular functions, including maintaining the electric potential of cells and muscle function.