Question

Which type of metal is used in cathodic protection of iron against rusting?

Answer 1

We know that iron undergoes corrosion or rusting in presence of moisture and air. Cathodic protection involves the coating of the metal surface with another metal which oxidizes before the other metal hence avoiding its corrosion.

Complete answer:
For corrosion to occur, three things are required, namely, an electrolyte, a metal surface and an electron acceptor. If any one of these necessary conditions is removed, corrosion can be prevented. Rusting in simplest terms is the oxidation of iron. Hence, to prevent its oxidation a more reactive metal should be used for coating the iron surface which prevents iron from oxidizing when kept open in air. Of the given metals, only zinc is more reactive than iron.
Cathodic protection to iron is provided by applying a layer of zinc on the surface of iron. This process is known as galvanization and is a very common and effective method to prevent the rusting of iron. Zinc being more reactive than iron reacts with oxygen preferentially. Anodic protection involves the coating of the iron or its alloy with a less active metal, like tin
Therefore, the metal which is more electropositive than iron such as $Al\text{ },\text{ }Zn\text{ },\text{ }Mg$ can be used in cathodic protection of iron against rusting.

Note:
Remember that the process of galvanization is known as cathodic protection and zinc is the sacrificial anode in this process. Anodic protection can also be used to protect the metal from corrosion. The protective layer will not corrode, and thus the surface will be protected as long as the coating is in place.