Magnetite Fe3O4 (containing Fe^2+ and Fe^3+) is completely oxidised by an oxidising agent to Fe2O3, that is, all iron ends as Fe^3+. The n-factor of Fe3O4 in this change is

JEE Advanced levelSingle correct optionDifficulty 3 of 3rx100

Magnetite $Fe X_{3} O X_{4}$ (containing $Fe X^{2 +}$ and $Fe X^{3 +}$ ) is completely oxidised by an oxidising agent to $Fe X_{2} O X_{3}$ , that is, all iron ends as $Fe X^{3 +}$ . The n-factor of $Fe X_{3} O X_{4}$ in this change is

Fe X_{3} O X_{4}

FeO \cdot Fe X_{2} O X_{3}

: one

Fe X^{2 +}

and two

Fe X^{3 +}

per formula unit. Only the

Fe X^{2 +}

changes (to

Fe X^{3 +}

), losing 1 electron. Using average oxidation number gives the same: 3 x (3 - 8/3) = 1.