Answer
$\therefore\text{iron(III) carbonate molecular formula will be}$ $Fe_2(CO_3)_3$
Work Step by Step
$\text{iron(III) is having a charge of +3}$
$\text{carbonate is having a charge of +2}$
$\therefore\text{iron(III) carbonate molecular formula will be}$ $Fe_2(CO_3)_3$