In a typical fuel cell,the reactant $(R)$ and product $(P)$ are

When does the galvanic cell become an electrolytic cell?

Which statement is correct for a fuel cell?

Under what condition is $E_{cell} = 0$ or $\Delta_r G = 0$?

In the button cells widely used in watches and other devices,the following reaction takes place:
$Zn_{(s)} + Ag_2O_{(s)} + H_2O_{(l)} \rightarrow Zn^{2+}_{(aq)} + 2Ag_{(s)} + 2OH^{-}_{(aq)}$
Determine $\Delta_r G^\Theta$ and $E^\Theta$ for the reaction.

The standard free energy change $(\Delta G^{\circ})$ for the following reaction (in $kJ$) at $25^{\circ} C$ is $3 Ca_{(s)} + 2 Au^{3+}(aq, 1 M) \rightarrow 3 Ca^{2+}(aq, 1 M) + 2 Au_{(s)}$ (given: $E^{\circ}_{Au^{3+}/Au} = +1.50 \ V, E^{\circ}_{Ca^{2+}/Ca} = -2.87 \ V, 1 \ F = 96500 \ C \ mol^{-1}$)