Sacrificial Protection by Zinc Coating

Steps:

• Recall that painting iron provides a barrier but fails if scratched, exposing iron to corrosion.
• Understand galvanization uses zinc, which is more reactive than iron in the reactivity series.
• Compare: zinc acts as a sacrificial anode, corroding preferentially to protect iron even if damaged.
• Eliminate options not explaining damage protection.

Why A is correct:

• Zinc provides cathodic protection, where it corrodes sacrificially (as the anode) instead of iron (cathode), per electrochemical series principles.

Why the others are wrong:

• B: Zinc above iron explains reactivity but not damage protection mechanism.
• C: Zinc does react with air and water, forming a protective layer, but that's not the key advantage over painting.
• D: Zinc and iron do not form an unreactive alloy; it's a physical coating.

Final answer: A