$K, Ca$ and $Li$ metals may be arranged in the decreasing order of their standard electrode potentials as

Given the following standard electrode potentials:
$Cu^{+2} + 2e^{-} \to Cu$,$E^{o} = X_{1}$
$Cu^{+} + e^{-} \to Cu$,$E^{o} = X_{2}$
Calculate the standard electrode potential $E^{o}$ for the reaction: $Cu^{+2} + e^{-} \to Cu^{+}$

If $E_{Au^{+}/Au}^o$ is $1.69 \text{ V}$ and $E_{Au^{3+}/Au}^o$ is $1.40 \text{ V}$,then $E_{Au^{+}/Au^{3+}}^o$ will be ... $\text{V}$.

Which is the increasing order of reducing power of the following metals on the basis of standard electrode potential? $Ag^{+}/Ag = 0.80 \ V$,$Mg^{2+}/Mg = -2.37 \ V$,$Hg^{2+}/Hg = 0.79 \ V$,$Cr^{3+}/Cr = -0.74 \ V$

The standard electrode potentials of the half-cells are given below:
$Zn^{2+} + 2e^- \to Zn$; $E^{\circ} = -0.76 \, V$
$Fe^{2+} + 2e^- \to Fe$; $E^{\circ} = -0.44 \, V$
The $EMF$ of the cell $Fe^{2+} + Zn \to Zn^{2+} + Fe$ is ............ $V$.

Write a note on the standard hydrogen electrode $(SHE)$.