RUSTING (YR10)

The results of our rusting experiment:

The tube on the left has a stopper, and a small amount of Calcium Chloride to exclude and absorb any air (Oxygen)
This nail has no rust.

The middle tube has no stopper and is half-full of plain water. The nail is therefore open to reaction with Oxygen and Water. This nail had a lot of rusting.
The tube on the right is filled with boiled water (to remove dissolved Oxygen) and covered with a layer of oil. This nail had only a very small amount of rust

Conclusion:

Both Oxygen and Water (as well as Iron, of course! - Thanks to Ken "what's the frequency?" Lockhart) are needed for rusting to occur.

Wikipedia link