Question

Why galvanised metals donot corrode even after the zinc is gone?

Answer 1

If the zinc coating is broken, the galvanized object remains protected against rusting because zinc is more reactive

Answer 2

Zinc is more reactive than iron, and loses electrons more easily. The outer layer of zinc of any galvanized material, reacts with the atmospheric oxygen to form Zinc Oxide (ZnO), which is stronger than Zinc.

hope it helps..