Which of the following metals could be used as sacrifical anode for preventing the corrosion of iron?

Step 1: Analyze the question We need a metal that can act as a sacrificial anode to protect iron from corrosion (rusting).

Step 2: The concept Corrosion of iron is an oxidation process: Fe → Fe²⁺ + 2e⁻. In sacrificial protection (a type of cathodic protection), iron is connected to a more reactive metal. The more reactive metal:

• loses electrons more readily (it is oxidized instead of iron),
• corrodes in place of the iron, "sacrificing" itself,
• supplies electrons to the iron, which prevents the iron from oxidizing.

So the sacrificial metal must be higher than iron in the electrochemical (reactivity) series.

Step 3: Compare the options The reactivity series (most to least reactive): K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Ag, Au

• A. Copper: below iron, so less reactive. Iron would corrode instead. ❌
• B. Lead: below iron, so less reactive. ❌
• C. Magnesium: above iron, so more reactive. It is oxidized in preference to iron. ✅
• D. Silver: well below iron. ❌

Step 4: Reasoning with electrode potentials

• Mg²⁺/Mg: E° = −2.37 V
• Fe²⁺/Fe: E° = −0.44 V

Magnesium has the more negative potential, so it is the better reducing agent and acts as the anode: Mg → Mg²⁺ + 2e⁻

The electrons flow to the iron, keeping it protected.

Answer: C. Magnesium

Tip: For sacrificial protection, remember "the bodyguard must be stronger than the VIP": the protecting metal must be more reactive than iron. Magnesium and zinc are the usual choices. Zinc is used in galvanizing, and magnesium blocks are attached to ship hulls and underground pipelines. Any metal listed below iron in the series (Cu, Pb, Ag) will never work.