For the decomposition of $Al_2O_3$ at $500^{\circ}C$,the free energy change is $\frac{2}{3} Al_2O_3 \to \frac{4}{3} Al + O_2$,$\Delta G = +966 \ kJ \ mol^{-1}$. The potential difference required for the electrolytic reduction of $Al_2O_3$ at $500^{\circ}C$ is ........... $V$.

The standard electrode potential $(E^o)$ of $Cu^{2+}/Cu$ is $+0.34 \, V$,while that of $Zn^{2+}/Zn$ is $-0.76 \, V$. Explain the reason for this difference.

Given are $E^{\circ}$ values for some half reactions:
$I_2 + 2e^{-} \to 2I^{-}$ ; $E^{\circ} = 0.54 \, V$
$MnO_4^{-} + 8H^{+} + 5e^{-} \to Mn^{2+} + 4H_2O$ ; $E^{\circ} = 1.52 \, V$
$Fe^{3+} + e^{-} \to Fe^{2+}$ ; $E^{\circ} = 0.77 \, V$
$Sn^{4+} + 2e^{-} \to Sn^{2+}$ ; $E^{\circ} = 0.1 \, V$
The strongest reducant and oxidant respectively are:

Calculate $E^o_{cell}$ for the following cell in $V$:
$Zn_{(s)} | Zn^{2+}_{(aq.)} || Ag^{+}_{(aq.)} | Ag_{(s)}$
Given: $E^o_{Zn^{2+}/Zn} = -0.76 \ V$ ; $E^o_{Ag^{+}/Ag} = 0.80 \ V$

Electrode potentials $(E^o)$ are given below:
$Cu^{+}/Cu = +0.52 \ V$
$Fe^{3+}/Fe^{2+} = +0.77 \ V$
$\frac{1}{2} I_{2(s)}/I^{-} = +0.54 \ V$
$Ag^{+}/Ag = +0.88 \ V$
Based on the above potentials,the strongest oxidizing agent will be:

Calculate the $emf$ of the cell $Cu_{(s)} | Cu^{2+}_{(aq)} || Ag^+_{(aq)} | Ag_{(s)}$. Given: $E^0_{Cu^{2+}/Cu} = +0.34 \ V$,$E^0_{Ag^+/Ag} = +0.80 \ V$.