Does rust need water and air?

How to read this

Each tube holds an identical iron nail. What differs is what each nail is exposed to. Drag the day slider — all four tubes age together — and watch which ones actually rust.

Why each tube is set up this way

• Tube A is the "everything present" case — the control that shows rusting can happen at all.
• Tube B keeps water but removes air: boiling water drives out dissolved oxygen, and a floating layer of oil stops more air from dissolving back in.
• Tube C keeps air but removes water: a drying agent (anhydrous calcium chloride) soaks up any moisture before it can reach the nail.
• Tube D is yours — try every combination and confirm the rule for yourself: rust needs water and oxygen, together, or it doesn't form at all.