For the spontaneity of a cell,which of the following is correct?

Calculate $\Delta G^{\circ}$ for the cell: $Sn_{(s)} | Sn^{2+}_{(1M)} || Ag^{+}_{(1M)} | Ag_{(s)}$ at $25^{\circ} C$ given that $E^{\circ}_{cell} = 0.90 \ V$. (in $kJ$)

$FeO_4^{2-}$ $\xrightarrow{2.2 \ V} Fe^{3+}$ $\xrightarrow{0.70 \ V} Fe^{2+}$ $\xrightarrow{-0.45 \ V} Fe^0$
$E_{FeO_4^{2-} / Fe^{2+}}^{\theta}$ is $x \times 10^{-3} \ V$. The value of $x$ is $.........$.

The standard electrode potential for the half-cell reactions are
$Zn^{2+} + 2e^{-} \longrightarrow Zn ; E^{\circ} = -0.76 \ V$
$Fe^{2+} + 2e^{-} \longrightarrow Fe ; E^{\circ} = -0.44 \ V$
The $emf$ of the cell reaction,
$Fe^{2+} + Zn \longrightarrow Zn^{2+} + Fe$ is

The correct order of reduction potentials of the following pairs is
$A.$ $Cl_2 / Cl^{-}$
$B.$ $I_2 / I^{-}$
$C.$ $Ag^{+} / Ag$
$D.$ $Na^{+} / Na$
$E.$ $Li^{+} / Li$
Choose the correct answer from the options given below.

Which reference electrode is used to measure the electrode potential of other electrodes?