Question

Fe + O2--->FeO?

Answer 1

To "balance" the equation you need to change the coefficients of the compounds.
`2Fe + O_2 -> 2FeO`

Explanation:

This is ONE of the possible iron oxidations. The other common one is:
`4Fe + 3O_2 -> 2Fe_2O_3`

Answer 2

Well, that's almost correct, but not yet balanced.

Explanation:

The full balanced equation is as below:
`2Fe+O_2->2FeO`
Where the iron ion is an iron (II) ion, simply because it is easier to balance equations for iron (II) ions compared to iron (III) ions.

This equation you are seeking is an oxidation equation, where iron metal is oxidised by oxygen gas. This can be represented in two half-equations.
`2Fe->2Fe^(2+)+4e^(-)`
Where `e^-` refers to the two valence electrons from each iron atom to be used in bonding.
`O_2+4e^(-)->2O^(2-)`
Therefore, after getting two iron (II) ions and two oxygen ions from these two half-equations, you can put them together to get:
`2Fe+O_2->2FeO`

Hope this helps!