Iron objects such as storage tanks and underground pipelines can be protected from corrosion by?

Question

Iron objects such as storage tanks and underground pipelines can be protected from corrosion by
connecting them through a wire to a piece of
A) Pb
B) Ag
C) Sn
D) Mg

Answer 1

Mg, magnesium, which will act as a sacrificial anode and corrode in preference to the iron, which becomes the cathode in the cell formed by the two metals and the conducting earth. The piece of Mg must also be underground and nearby. See the ref.