Which are considered depolarizers in cathodic protection?

In the context of cathodic protection, depolarizers are substances that help facilitate the reduction reactions, which counteract the polarization effects that can arise during electrochemical processes. Water flow, microbiological activity, and dissolved oxygen are all significant as they play a critical role in the depolarization of metallic surfaces.

Water flow can enhance the transfer of ions, which supports the chemical reactions required for depolarization. Microbiological activity is also crucial because certain microbes can produce metabolic byproducts that act as depolarizers, effectively promoting the cathodic reactions that protect the metal surface. Dissolved oxygen is an essential element as it is often involved in cathodic reaction processes; when oxygen is present, it can be reduced at the cathode, promoting further cathodic protection.

In contrast, the other options consist of different ions and substances that do not effectively serve as depolarizers in the cathodic protection context. While they may include ions or compounds that are relevant in other electrochemical reactions, they do not fit the role of depolarizers in the cathodic protection system where the primary goal is to mitigate corrosion by promoting cathodic reactions through the reduction of polarization effects.