Iron (II) means that Fe has lost two electron i.e Fe⁺².
We also know that Oxygen normally exists in -2 oxidation state i.e. O⁻².
And, for a neutral Iron (II) Oxide the overall charge on it must be zero.
So,
+ 2 + (-2) = 0
Means,
For one atom of Fe⁺² we need one atom of O⁻².
FeO
Result:
One Iron (II) ion combines with oxygen to form iron(ii) oxide.
