If $E_1^0,E_2^{0}and{E}_3^0$  are standard oxidation potentials for $Fe|F{e}^{2+},F{e}^{2+}|F{e}^{3+}andFe|F{e}^{3+},$ then $E_3^0=\frac{E_2^0+2E_1^0}{n}.$ The value of n is……….

$Fe\to F{e}^{2+}+2e^{-};E_1^0$

$F{e}^{2+}\to F{e}^{3+}+e^{-};E_1^0$

Adding (1) and (2), we have $Fe\to F{e}^{3+}+3e^{-};E_1^0$

$\Delta G_1^0=-2F{E}_1^0, \Delta G_2^0=-1F{E}_2^0, \Delta G_3^0=\Delta G_1^0+\Delta G_2^0$

$-3F{E}_3^0=-2F{E}_1^0-1F{E}_2^0$

$E_3^0=\frac{E_2^0+2E_1^0}{3}$