Which of the following ions does the sodium-potassium pump primarily export out of the cell?

The sodium-potassium pump, an essential membrane protein, primarily functions to maintain the electrochemical gradient across the plasma membrane of cells. This pump actively transports sodium (Na+) ions out of the cell and potassium (K+) ions into the cell. Specifically, for every three sodium ions it exports, it imports two potassium ions.

Thus, when considering the question about which ion is primarily exported, the option that represents the export of three sodium ions, which occurs with each cycle of the pump's activity, is distinctly correct. The primary role of this pump is crucial for various cellular processes, including maintaining osmotic balance and facilitating action potentials in nerve cells.

The other ions mentioned do not relate to the primary function of the sodium-potassium pump. Calcium and magnesium ions do not play a direct role in its operation. The pump notably targets sodium and potassium specifically in the process of maintaining cellular homeostasis.