Final answer:
The correct option is C. The anode rod in a water heater serves to prevent corrosion of the tank by acting as a sacrificial anode. Made from metals like zinc or magnesium, it undergoes oxidation to protect the steel tank, requiring periodic replacement to maintain effectiveness.
Step-by-step explanation:
The purpose of an anode rod in a water heater is to prevent corrosion of the tank. Anode rods are made from a more active metal than the steel of the tank, such as zinc or magnesium. These metals offer cathodic protection by acting as sacrificial anodes.
They corrode over time instead of the tank itself, due to their lower reduction potential, meaning as they oxidize, they protect the tank from rusting and corrosion, effectively extending its useful lifetime. The metal of the tank becomes the cathode and does not react but conducts the electrons from the oxidation process of the anode rod. Saltwater can speed up corrosion, but the anode rod helps to slow down this process. It is important to monitor and replace the anode rod periodically to ensure continued protection of the water heater tank.