So it needs to be a practical experiment which you can perform and you need to produce Iron metal and Oxygen gas from the Iron (III) Oxide……hmmmm
The first thing that comes to mind would be to do a single replacement reaction with the Iron Oxide and a more active metal (like Aluminum, for example), to produce the Iron metal and leaving another metal Oxide. You could then melt and electrolytically refine the metal oxide back to the original metal and in the process give off Oxygen gas.
Fe2O3 + 2Al --> 2Fe + Al2O3
Al+3 + 3e- --> Al
2O-2 --> O2 + 4e-
But I suppose you could have cut the thermite process out and saved yourself a step by just melting and electrolysizing the Fe2O3 directly (if it wouldn’t decompose first), but neither Fe2O3 or Al2O3 melt at very reasonable temperatures, so this method isn’t too practical.
Another method that comes to mind would be to use Carbon to reduce the Iron in the Iron Oxide back to its elemental state while producing Carbon Dioxide gas.
2 Fe2O3 + 3 C --> 4 Fe + 3 CO2
One could then collect this Carbon Dioxide gas and (using a plant’s photosynthetic abilities) produce Oxygen gas and some sugar….or some other method of breaking up the CO2 back into Carbon and Oxygen gas.
I guess this isn’t too practical of an idea either.
Getting the Iron metal back is relatively easy….it is getting the Oxygen back which is posing a problem in my ideas.
But some plants release ethylene gas (C2H4) besides the oxygen and water vapor which may contaminate the sample. But unless you are using a dandelion or a plant with a fruit on it i wouldn't be too worried. If you use aluminum keep the temperature below 2204 degrees celcius because that could initate a thermite reaction and you can't put those out with water. Go do some research before you get into it too deeply.