If the zinc coating is broken, the galvanised object remains protected against rusting because zinc is more reactive than iron and hence can be easily oxidised . Thus when zinc layer breaks down, the zinc continues to react and gets oxidised . Hence iron is protected.

Why galvanized articles are protected even when scratched?

Galvanising forms a coating of corrosion-resistant zinc which prevents corrosive substances from reaching the more delicate metal. the zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed steel will still b protected by the remaining zinc.

Why is galvanised iron protected from rusting?

Galvanizing protects from rust in a number of ways: It forms a barrier that prevents corrosive substances from reaching the underlying steel or iron. ... The zinc protects its base metal by corroding before iron. The zinc surface reacts with the atmosphere to form a compact, adherent patina that is insoluble in rainwater.