Which element is reduced at the cathode of a Clark polarographic electrode?

The cathode of a Clark polarographic electrode is designed to detect the partial pressure of dissolved oxygen in a solution. In electrochemical terms, reduction refers to the gain of electrons, and at the cathode, the process involved is the reduction of oxygen molecules to hydroxyl ions. The specific reaction that occurs is:

[ O_2 + 4e^- + 2H_2O \rightarrow 4OH^- ]

This reaction indicates that oxygen serves as the electron acceptor at the cathode, and thus it is effectively reduced during the electrochemical process.

In contrast, the other elements mentioned do not undergo reduction at the cathode of this specific electrode configuration. Silver, chloride, and potassium do not play a role in the operational mechanics of the Clark electrode, which is specifically focused on measuring oxygen levels. This makes the recognition of oxygen as the reduced element at the cathode critical in understanding the electrode's function in clinical chemistry applications.