Iron does not rust even if Zinc coating is broken in a galvanized iron pipe but rusting occurs much faster if tin coating over iron is broken. Explain.
Fe is less electropositive than Zn. So, as long as Zn is on the surface of the Fe pipe then Zn acts as an anode and the Fe pipe acts as a cathode. As a result of this, rusting of Fe is prevented by Zn. On the other hand, Zn is more electropositive than Sn, which protects iron until the Sn coating is unbroken. If any pores or breaks are observed, even tin is there the exposed iron gets rusted.
