How can zinc prevent iron from rusting ? Pls explain what are the properties of zinc which do not let iron to rust

Galvanization, or galvanisation, is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanization, in which parts are submerged in a bath of molten zinc. Galvanizing protects in two ways:
 
 
It forms a coating of corrosion-resistant zinc which prevents corrosive substances from reaching the more delicate part of the metal. 
The zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed steel will still be protected by the remaining zinc.