化學問題-2(急！)(10分)

There are two sets of apparatus, so 1 set is for the experiment, and the other set is for the control.
so 1 set of apparatus is for the experiment is :
1 test tube, 1 clean iron nails, tap water and paraffin oil
the other set apparatus for the control (對照實驗) is :
1 test tube, 1 clean iron nails, tap water (boiled and cool down) and paraffin oil.

Firstly, to setup the experiment apparatus:
Put one clean iron nail into the test tube, then add in tap water to totally cover the iron nail. On the top of the tap water, pour in a layer of paraffin oil. The layer of the paraffin oil is to prevent the air in the tap water to diffuse in and out from the experiment setup, as normal cool tap water consists of air. Then put the test tube setup aside.
Secondly, to setup the control apparatus:
Pour in some tap water into another test tube while the volume of the tap water is a bit more to cover the clean iron nail when it put into. Don't put the clean iron nail inside at this moment. Just switch on the gas to light up the Bunsen Burner. Use the test tube holder to handle the test tube and place the tube on the fire of the Bunsen Burner. Wait for the tap water to boil. Let the tap water boiling for a moment, so that the air in the tap water is removed under boiling. Then switch off the Bunsen burner, and let the water and test tube cooled to room temperature. When the apparatus is cooled, insert the clean iron nail into the test tube and cover the boiled tap water with a layer of paraffin oil. As the first step, the paraffin oil layer is to prevent the diffusion of air into the control setup to alternate the condition.
Finally, put both test tubes together in a cool place for a few days.
Then the result will be shown. The unboiled tap water will causes the clean iron nail to rusted, and the boiled tap water causes no effects to the clean iron nail.
The conclusion is that air is the necessary for the rusting of iron, since both setup are the similiar conditions except only air was removed from the control setup.
As the clean iron nail rusted only when air presented, then that is one of the essential conditions for the rusting.