Consider the three electrodes $\mathrm{Fe} / \mathrm{Fe}^{2+}, \mathrm{Fe} / \mathrm{Fe}^{3+}$, and $\mathrm{Fe}^{2+} / \mathrm{Fe}^{3+}$, for which the standard electrode (oxidation) potentials are: $E_1^0, E_2^0$, and $E_3^0$, respectively. The standard EMF of the cell, $\mathrm{Fe} / \mathrm{Fe}^{2+} \| \mathrm{Fe}^{3+}+\mathrm{Fe}$, is $E_4^0$. The correct expression(s) is (are):

• Correct answer
  A

  $E_3^0=\left(3 E_2^0-2 E_1^0\right)$
• B

  $E_3^0=\left(E_2^0-E_1^0\right)$
• C

  $E_4^0=\left(2 E_1^0-3 E_2^0\right)$
• Correct answer
  D

  $E_4^0=\left(E_1^0-E_2^0\right)$

Hence, the correct answer is options: 'A', 'D'.