Which metal is considered more active in cathodic protection?

The correct answer identifies that new steel in fresh water is considered more active for cathodic protection purposes. In the cathodic protection context, the term "more active" refers to the tendency of a metal to oxidize, which means it is more prone to corrosion, particularly in comparison to other metals that may be present.

Fresh water environments, particularly in the case of new steel, generally allow for a more pronounced electrochemical reaction, enhancing the sacrificial nature of any anodes attached to it. New steel has less oxidation and impurities compared to older steel, making it more susceptible and reactive in a corrosive environment. This reactivity can be utilized effectively by sacrificial anodes such as zinc or magnesium, which preferentially corrode rather than the new steel structure, thereby protecting it.

In contrast, while old steel, aluminum, and stainless steel have their own behaviors in different environments, they do not match the level of activity in corrosion reactions seen with new steel in fresh water, particularly when considering the application of cathodic protection. This deeper insight into the characteristics of metals in various conditions illustrates why new steel in fresh water is the most active choice regarding cathodic protection strategies.