Iron can be protected from corrosion by coating the surface with?

Analyze the question: The question asks which metal can be coated on iron to protect it from corrosion (rusting).

Concept: Iron rusts when it reacts with oxygen and water. Coating it with another metal can protect it in two ways:

1. Barrier protection: the coating keeps air and moisture away from the iron.
2. Sacrificial protection: if the coating is a metal more reactive than iron, it corrodes in place of the iron, even when the coating is scratched.

Reactivity series (high to low): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au

Step-by-step evaluation:

• A. Gold: Less reactive than iron. It is far too expensive for this use, and if scratched, the iron would corrode faster.
• B. Silver: Less reactive than iron, and also too expensive. Scratches would speed up rusting of the iron.
• C. Copper: Less reactive than iron. If the coating is broken, iron becomes the anode and rusts even faster.
• D. Zinc: More reactive than iron, so it acts as a sacrificial metal. It is also cheap. Coating iron with zinc is called galvanizing, which is how galvanized roofing sheets ("zinc") are made.

Answer: D. zinc

Tip: Remember "Galvanize = Zinc". A protective metal for iron must be more reactive than iron, so it sits above Fe in the reactivity series. Tin and chromium plating are also used, but they give only barrier protection.