Which term describes a cathode?

The term that best describes a cathode is "noble." In the context of electrochemistry and cathodic protection, a noble metal is one that is relatively resistant to corrosion and oxidation. Noble metals, such as gold, platinum, and silver, do not easily lose electrons and participate in oxidation reactions.

In cathodic protection systems, the cathode is the site of reduction where electrons are accepted, thus preventing the oxidation of the anode, which usually consists of a more reactive or less noble material. The nobility of the cathode is essential because it helps maintain its integrity while protecting the more active anode from corrosion.

The other terms—like inert, active, and reactive—do not fully capture the most important characteristic of a cathode in the specific context of cathodic protection, which is its role in facilitating reduction reactions and its resistance to corrosion. An inert electrode, for instance, does not participate in chemical reactions, and active or reactive materials tend to corrode more readily. Hence, "noble" is the most appropriate descriptor for a cathode in the context of cathodic protection.