The Gibb's energy for the decomposition of Al₂O₃ at 500^oC is as follows
$${2 \over 3}$$ Al₂O₃ $$ \to $$ $${4 \over 3}$$ Al + O₂
$$\Delta $$_rG = +960 kJ mol^$$-$$1
The potential difference needed for the electrolytic reduction of aluminium oxide (Al₂O₃) at 500^oC is at least

Standard reduction potentials of the half reactions are given below :
F_2(g) + 2e^$$-$$ $$ \to $$ 2F^$$-$$_(aq) ;   E^o = + 2.85 V
Cl_2(g) + 2e^$$-$$ $$ \to $$ 2Cl^$$-$$_(aq) ;   E^o = + 1.36 V
Br_2(l) + 2e^$$-$$ $$ \to $$ 2Br^$$-$$_(aq) ;   E^o = + 1.06 V
I_2(s) + 2e^$$-$$ $$ \to $$ 2I^$$-$$_(aq) ;  E^o = + 0.53 V

The strongest oxidising and reducing agents 23 respectively are

Limiting molar conductivity of NH₄OH
$$\left[ {} \right.$$i.e.  $$\Lambda _{m\left( {N{H_4}OH} \right)}^0$$$$\left. {} \right]$$ is equal to

A solution contains Fe²⁺, Fe³⁺ and I^$$-$$ ions. This solution was treated with iodine at 35^oC. E^o for Fe³⁺/Fe²⁺ is + 0.77 V and E^o for I₂/2I^$$-$$ = 0.536 V.
The favourable redox reaction is