Can $E_{cell}^o$ or $\Delta_r G^o$ for a cell reaction ever be equal to zero?

The standard reduction potential for $Li^{+}/Li$,$Zn^{2+}/Zn$,$H^{+}/H_2$ and $Ag^{+}/Ag$ is $-3.05$,$-0.762$,$0.00$ and $+0.80 \ V$. Which of the following has the highest reducing capacity?

The standard electrode potentials $(E^o)$ for $OCl^{-}/Cl^{-}$ and $\frac{1}{2}Cl_2/Cl^{-}$ are $0.94 \ V$ and $+1.36 \ V$ respectively,the $E^o$ value for $OCl^{-}/\frac{1}{2}Cl_2$ will be ........... $V$.

Given below are half-cell reactions:
$MnO_{4}^{-} + 8H^{+} + 5e^{-} \rightarrow Mn^{2+} + 4H_{2}O$,
$E^{o}_{MnO_{4}^{-} / Mn^{2+}} = +1.510 \, V$
$\frac{1}{2} O_{2} + 2H^{+} + 2e^{-} \rightarrow H_{2}O$,
$E^{o}_{O_{2} / H_{2}O} = +1.223 \, V$
Will the permanganate ion,$MnO_{4}^{-}$,liberate $O_{2}$ from water in the presence of an acid?

Calculate the $Zn-Cu$ cell (Daniell cell) potential. Given: $E^o_{Zn^{2+}|Zn} = -0.76 \ V$ and $E^o_{Cu^{2+}|Cu} = 0.34 \ V$. (in $V$)

For the half-reactions $Zn \rightarrow Zn^{2+} + 2e^{-}$ and $Fe \rightarrow Fe^{2+} + 2e^{-}$,the standard oxidation potentials are given as $E^{0}_{Oxi} = +0.76 \ V$ and $E^{0}_{Oxi} = +0.41 \ V$ respectively. Calculate the cell potential for the reaction $Fe^{2+} + Zn \rightarrow Zn^{2+} + Fe$ in $V$.