Which of the following reactions is used to make a fuel cell?

Given that
$E^o_{Ni^{2+} | Ni} = -0.25 \ V$
$E^o_{Cu^{2+} | Cu} = 0.34 \ V$
$E^o_{Ag^{+} | Ag} = 0.80 \ V$
$E^o_{Zn^{2+} | Zn} = -0.76 \ V$
Which of the following reactions under standard condition will not take place in the specified direction?

$A$ button cell used in watches functions as follows:
$Zn_{(s)} + Ag_2O_{(s)} + H_2O_{(l)} \rightarrow 2Ag_{(s)} + Zn^{2+}_{(aq)} + 2OH^{-}_{(aq)}$
If the half-cell potentials are:
$Zn^{2+}_{(aq)} + 2e^- \rightarrow Zn_{(s)} \,;\, E^o = -0.76 \, V$
$Ag_2O_{(s)} + H_2O_{(l)} + 2e^- \rightarrow 2Ag_{(s)} + 2OH^{-}_{(aq)} \,;\, E^o = 0.34 \, V$
The cell potential will be $..........$ $V.$

The Gibbs energy for the decomposition of $Al_2O_3$ at $500^oC$ is as follows:
$\frac{2}{3} Al_2O_3 \rightarrow \frac{4}{3} Al + O_2$
$\Delta_rG = +960 \ kJ \ mol^{-1}$
The potential difference needed for the electrolytic reduction of aluminium oxide $(Al_2O_3)$ at $500^oC$ is at least ........ $V$.

Which of the following formulae is used to obtain the value of $E_{\text{cell}}^{\circ}$ for a reaction taking place in a Dry cell?

In a $Cu-Zn$ cell,.....