1. Find the oxidation states of iron in $\mathrm{Fe_3O_4}$

   We can write: $\mathrm{Fe_3O_4 = FeO \cdot Fe_2O_3}$

   So in $\mathrm{Fe_3O_4}$:

   • 1 iron is in $+2$ state
   • 2 irons are in $+3$ state

2. Electrons needed to reduce iron ions to iron metal

   Reduction to metallic iron:

   • $\mathrm{Fe^{2+} + 2e^- \to Fe}$
   • $\mathrm{Fe^{3+} + 3e^- \to Fe}$

   Therefore, for 3 moles of Fe present in $\mathrm{Fe_3O_4}$, total electrons required are: $1\times 2 + 2\times 3 = 2 + 6 = 8\text{ mol e}^-$

3. Charge required per mole of iron

   Since 3 moles of Fe are obtained from 1 mole of $\mathrm{Fe_3O_4}$ using 8 moles of electrons, charge needed for 1 mole of Fe is: $\frac{8}{3}\text{ F} = 2.67\text{ F}$

4. Nearest integer

   $\frac{8}{3} \approx 2.67$ Nearest integer $= 3$

Final Answer

$\boxed{3}$