What is $emf$?

$A$ reaction,$Ni_{(s)} + Cu^{2+}_{(aq)} \rightarrow Ni^{2+}_{(aq)} + Cu_{(s)}$ occurs in a cell. Calculate $E^0_{cell}$ if $E^0_{Cu} = 0.337 \ V$ and $E^0_{Ni} = -0.257 \ V$. (in $V$)

For metals $A, B$ and $C$,the standard reduction potentials are $0.68 \ V, -2.50 \ V$ and $0.5 \ V$ respectively. What is the order of their reducing power?

Given $E_{Cu^{2+}/Cu^{+}}^o = 0.15 \, V$,$E_{Cu^{2+}/Cu}^o = 0.34 \, V$. The standard electrode potential for the half-cell $Cu^{+}/Cu$ is ............. $V$.

Calculate $E^o_{cell}$ for the following cell in $V$:
$Zn_{(s)} | Zn^{2+}_{(aq.)} || Ag^{+}_{(aq.)} | Ag_{(s)}$
Given: $E^o_{Zn^{2+}/Zn} = -0.76 \ V$ ; $E^o_{Ag^{+}/Ag} = 0.80 \ V$

The $EMF$ of a cell whose half-cell reactions are given below is .......... $V$.
$Mg^{2+} + 2e^- \to Mg_{(s)}; E^o = -2.37 \ V$
$Cu^{2+} + 2e^- \to Cu_{(s)}; E^o = +0.34 \ V$ (in $V$)