Final answer:
The polarographic electrode measures partial pressure of O2 through an oxygen-dependent chemical reaction that generates a current related to oxygen concentration.
Step-by-step explanation:
The polarographic electrode measures the partial pressure of O2 by relying on an oxygen-dependent chemical reaction. It involves a reduction process at the electrode surface where oxygen is reduced, and the resulting current is related to the oxygen concentration in the sample. Ion-selective electrodes function on a similar principle, monitoring the potential change related to the concentration of specific ions or molecules, which in the case of oxygen, is indicative of its partial pressure.