In oxygen concentration cell corrosion, the area with high cathodic activity will act as the

• A. Anode
• B. Electrode
• C. Ground
• D. Cathode

Answer: (D)

In this kind of corrosion setup, differences in oxidant concentration create a potential difference along the metal. The area that has more available oxygen will promote the reduction reaction (oxygen is reduced more readily there). That makes it the site where electrons are consumed, i.e., the cathode. The electrons flow from the less-oxygenated area through the metal toward the oxygen-rich area, so the low-oxygen region becomes the anode and corrodes. So the area with high cathodic activity acts as the cathode because it is where reduction dominates. Ground and a general electrode term don’t specify this role, and the cathode is the correct functional label for the high-oxygen area.