Which method is used to prevent steel and iron from rusting? 

Galvanization 

The correct answer is option 3. Galvanization.

The method used to prevent steel and iron from rusting is galvanization.

Galvanization is a process in which a protective layer of zinc is applied to the surface of steel or iron to prevent corrosion. This is achieved by immersing the steel or iron into a bath of molten zinc or by electroplating zinc onto the surface.

The zinc coating acts as a sacrificial anode, providing a barrier between the steel or iron substrate and the surrounding environment. When the galvanized steel or iron is exposed to moisture or oxygen, the zinc coating corrodes preferentially, protecting the underlying metal from rust or corrosion. So, the correct answer is: Galvanization