Why is alternating current used for measuring the resistance of an electrolytic solution?

Using the standard electrode potentials, predict if the reaction between the following is feasible: 
$\mathrm{F}{\mathrm{e}}^{3+}\left(\mathrm{a}\mathrm{q}\right)$ and ${\mathrm{I}}^{-}\left(\mathrm{a}\mathrm{q}\right)$

${\mathrm{E}}_{{\mathrm{Fe}}^{3+}/{\mathrm{Fe}}^{2+}}^{\circ }=+0.77 \mathrm{V}$, ${\mathrm{E}}_{{\mathrm{I}}_2/{\mathrm{I}}^{-}}^{\circ }=+0.54 \mathrm{V}$.

The following is a sketch of an electrolytic cell used in the extraction of aluminium:
 
(i) What is the substance of which the electrodes $\mathrm{A}$ and $\mathrm{B}$ are made?

(ii) At which electrode (A or B) is the aluminium formed?

(iii) What are the two aluminium compounds in the electrolyte C?

(iv) Why is it necessary for electrode B to be continuously replaced?

If $E_1^o,E_2^o$ and $E_3^o$ are standard oxidation potentials for $Fe|F{e}^{2+},F{e}^{2+}|F{e}^{3+}$ and $Fe|F{e}^{3+}$ then $E_3^o=(E_2^o+2E_1^o)/n.$

The value of $\mathrm{n}$ is?