Question

what is the stoichiometric formula for ferric carbonate

Answer 1

Explicitly showing the ferric oxidation state can be done with Roman numerals: Fe(III)2 (CO3)3. Note that FeCO3 gives the same (opposite) valence of one iron to one carbonate, so that is the formula for ferrous carbonate, Fe(II)CO3, siderite, which is not what was asked about.

Answer 2

Answer:

FeCO3......is the answer