The answer will be Zn , that is zinc is the best metal to protect iron.
The iron corrosion can be protected by various method in which zinc, Zn is used.
1. Gavanization:
In this method iron that is Fe is coated with zinc that is Zn. Zinc is more prone to oxidation than iron so it will oxidise and thus protects iron .
2. Cathodic protection:
In this method, Zinc or magnesium is used to protect iron, these metals are electrically connected to the iron. The more active metal that is zinc or magnesium over here is the sacrificial anode. And the iron metal is the cathode that remains unoxidized.