The $E^{0}_{Red}$ values of $A, B, C,$ and $D$ are $0.8 \, V, 0.79 \, V, 0.34 \, V,$ and $-2.37 \, V$ respectively. Which element can displace the other three from their salt solutions?

$Cr_2O_7^{2-} + I^{-} \to I_2 + Cr^{3+}$
$E^0_{cell} = 0.79 \ V$
$E^0_{Cr_2O_7^{2-}} = 1.33 \ V$,$E^0_{I_2}$ is ........... $V$

Using the standard electrode potential values,which of the following statements $(I, II, III, IV)$ is/are correct?
$Fe^{2+}_{(aq)} + 2e^{-} \rightleftharpoons Fe_{(s)}$ ; $E^o = -0.44 \, V$
$Cu^{2+}_{(aq)} + 2e^{-} \rightleftharpoons Cu_{(s)}$ ; $E^o = +0.34 \, V$
$Ag^{+}_{(aq)} + e^{-} \rightleftharpoons Ag_{(s)}$ ; $E^o = +0.80 \, V$
$I$. Copper displaces iron from $FeSO_4$ solution.
$II$. Iron displaces copper from $CuSO_4$ solution.
$III$. Silver displaces copper from $CuSO_4$ solution.
$IV$. Iron displaces silver from $AgNO_3$ solution.

The $E^{0}_{Red}$ values for $P, Q, R$ and $S$ are $-2.90 \, V, +0.34 \, V, +1.20 \, V$ and $-0.76 \, V$ respectively. The decreasing order of their reactivity is:

Given $:$
$(i) \, Cu^{2+} + 2e^- \rightarrow Cu \,, \, E^o = 0.337 \, V$
$(ii) \, Cu^{2+} + e^- \rightarrow Cu^{+} \,, \, E^o = 0.153 \, V$
Electrode potential,$E^o$ for the reaction,
$Cu^{+} + e^- \rightarrow Cu \,,$ will be $............$ $V$.

Which of the following equations represents the cell potential?