Iron can be protected from corrosion by coating the surface with

Correct answer: zinc.

Explanation: Iron is commonly protected by galvanizing—coating with zinc. Zinc is more reactive than iron, so it acts as a sacrificial anode: even if the coating is scratched, zinc preferentially corrodes, protecting the underlying iron. It also forms a tight oxide/carbonate film that slows further corrosion.

• Gold / Silver — Noble (less reactive) and expensive; if the coating is damaged, a galvanic couple forms and iron can corrode faster at exposed spots.
• Copper — More noble than iron; contact with iron promotes galvanic corrosion of the iron at flaws.
• Zinc — Correct; provides sacrificial (cathodic) protection and is the standard industrial method.