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

The standard reduction potentials for $Al^{3+} | Al$,$Fe^{2+} | Fe$,and $Br_2 | Br^-$ are $-1.66 \ V$,$-0.45 \ V$,and $1.09 \ V$ respectively. What is the correct order of their reducing power?

At $25^\circ C$,$1 \, atm$ of gas $X$ is bubbled through a solution containing $1 \, M$ $Y^-$ and $1 \, M$ $Z^-$. If the reduction potential order is $Z > Y > X$,then:

$E^o$ values of $Mg^{2+}/Mg$,$Zn^{2+}/Zn$ and $Fe^{2+}/Fe$ are $-2.37 \ V$,$-0.76 \ V$ and $-0.44 \ V$ respectively. Which of the following statements is correct?

Calculate the standard electromotive force $(E^o_{cell})$ for the following cell: $Zn|Zn^{2+} (1 \ M)||I^{-} (1 \ M)|CuI|Cu$. Given the half-cell reactions:
$CuI_{(s)} + e^{-} \to Cu_{(s)} + I^{-}_{(aq)}$ ; $E^o = -0.17 \ V$
$Zn^{2+}_{(aq)} + 2e^{-} \to Zn_{(s)}$ ; $E^o = -0.76 \ V$ (in $V$)

For the reaction $H_2 (1 \, bar) + 2AgCl_{(s)} \rightleftharpoons 2Ag_{(s)} + 2H^{+} (0.1 \, M) + 2Cl^{-} (0.1 \, M)$,$\Delta G^o = -48,250 \, J$ at $25 \, ^oC$. The standard emf of cell in which the given reaction takes place is ................. $V$