Rusting is the formation of hydrated iron (III) hydroxide from iron, in the presence of oxygen and water.

Thus, the conditions required for rusting are:
- oxygen (or air)
- water

Ways to prevent rusting

1. Painting/ greasing
2. Coating iron with a less reactive metal (e.g tin). However, once this layer is scratched, iron is exposed and will rust readily.
3. Sacrificial protection method (using e.g. magnesium and zinc). These more reactive metal will react in place of iron, thus protecting iron. The disadvantage is that once these more reactive metals have been used up, they need to be replace.
4. Forming alloys such as stainless steel

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