FeCO3 oxidation formulation help

Hi there,
I did an exercise and when we corrected it I realised that the oxidation number of Fe was (ll) but I don't know how can I find it.
The common name is iron (ll) nitrate and the other name, that I don't know how is called because i study this in basque, is iron (2+) nitrate trioxide (2-)

Please show the calculation you used and any other useful context

No, it is not 5.

Plus, you listed FeCO₃, but then you referred to the nitrate, so it is quite difficult to help, as in reality we don't know what the problem really is.