What element is reduced at the cathode of a Clark electrode?

In the operation of a Clark electrode, which is primarily used for measuring oxygen concentration in various environments, oxygen is the key element that gets reduced at the cathode. This reduction occurs through a redox reaction where oxygen gains electrons, resulting in the formation of hydroxide ions. The polarographic mechanism allows for the quantification of the partial pressure of oxygen based on this reduction process.

When an electric current is applied, oxygen molecules are drawn to the electrode surface, where they undergo reduction. The electrochemical reaction is essential for the functioning of the Clark electrode and is central to its application in clinical laboratories, particularly for measuring dissolved oxygen levels in blood and other fluids. This process emphasizes the role of oxygen as the primary analyte in this context.

The other options listed do not directly participate in the reduction process at the cathode of a Clark electrode. Carbon dioxide, glucose, and potassium are not involved in this particular electrode's electrochemical reaction mechanism for oxygen measurement.