How can iron be protected from rusting by an electrochemical method?

The correct answer is Option (1) → By connecting it to a more electropositive metal, which acts as a sacrificial electrode

• Rusting is an electrochemical process: at the spot that acts as the anode, iron is oxidised, \( \ce{Fe(s) -> Fe^2+(aq) + 2e^-} \).

• If iron is joined to a more electropositive metal such as Mg or Zn (E° −2.36 V and −0.76 V, lower than −0.44 V for \( \ce{Fe^2+/Fe} \)), that metal is oxidised in place of iron. It corrodes itself and saves the iron: it is a sacrificial electrode.

Why the other options are incorrect

Option (2) By connecting it to a more electropositive metal, which makes iron the anode — Incorrect. The more electropositive metal is oxidised more readily, so it becomes the anode; iron does not.

Option (3) By connecting it to a less electropositive metal, which makes iron the anode — Incorrect. Iron as the anode is the metal that is oxidised, so it would rust faster, not be protected.

Option (4) By connecting it to a less electropositive metal, which acts as a sacrificial electrode — Incorrect. A less electropositive metal is harder to oxidise than iron, so it cannot corrode in place of iron.

NCERT (2026-27 edition):
2.8 Corrosion – “… An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn, etc.) which corrodes itself but saves the object.”