Final answer:
PO2 electrodes are polished using coarse materials like pumice to increase sensitivity. Factors that limit null measurement accuracy include electrical noise, dissolved impurities, and instrumental calibration errors. Using a more sensitive digital device can improve accuracy.
Step-by-step explanation:
PO2 electrodes are often polished using a coarse material like pumice to increase sensitivity. The rough surface created by pumice allows for better contact between the electrode and the sample, leading to improved detection of oxygen concentration.
Factors that might limit the accuracy of null measurements include electrical noise, dissolved impurities in the sample, and instrumental calibration errors. A digital device that is more sensitive than a galvanometer can improve the accuracy of null measurements by reducing the impact of electrical noise and enhancing the precision of the measurement.