Which electrode is used to measure the electrode potential of any electrode?

$E^{\circ}_{Fe^{2+}/Fe} = -0.441 \ V$ and $E^{\circ}_{Fe^{3+}/Fe^{2+}} = 0.771 \ V$,the standard $EMF$ of the reaction $Fe + 2Fe^{3+} \rightarrow 3Fe^{2+}$ will be $.......... \ V$.

If the standard reduction potentials of four electrodes $A$, $B$, $C$, and $D$ are $+2.5 \text{ V}$, $+3.0 \text{ V}$, $-2.0 \text{ V}$, and $-1.5 \text{ V}$ respectively, in which of the following cases is the standard $emf$ of the cell maximum?

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 $kJ$)

For the cell reaction,$2Ce^{4+} + Co \to 2Ce^{3+} + Co^{2+}$,$E_{cell}^o$ is $1.89 \, V$ and $E_{Co/Co^{2+}}^o = +0.28 \, V$. If $E_{Ce^{4+}/Ce^{3+}}^o = x$,then $x$ is ............. $V$.

The standard electrode potential (in $V$) values for $Al^{3+}/Al$ and $Tl^{3+}/Tl$ are respectively: