The correct answer is option 1: Zinc is more electropositive than iron.

Electropositivity refers to the tendency of an element to lose electrons and form positive ions. In the context of corrosion, zinc is more electropositive than iron, meaning it has a higher tendency to lose electrons and ionize.

When zinc and iron are in contact, the zinc atoms will actively lose electrons and form zinc ions, while the iron atoms will gain those electrons and form iron ions. This process is known as galvanic corrosion. Since zinc is more electropositive, it acts as a sacrificial anode, protecting the iron from corrosion by sacrificing itself.

When a layer of zinc is present on the surface of iron, it will corrode first, creating a protective barrier that prevents the iron underneath from getting corroded. This process is known as galvanization and is commonly used to protect iron or steel structures from rust and corrosion.

Therefore, the primary reason zinc is used to protect iron from corrosion is because zinc is more electropositive than iron. It actively prevents the corrosion of iron by sacrificing itself as a sacrificial anode.