$MnO_4^- (aq) + 8H^+ (aq) + 5e^- \to Mn^{2+} (aq) + 4H_2O (l)$; $E_1^o = 1.51 \ V$
$MnO_2 (s) + 4H^+ (aq) + 2e^- \to Mn^{2+} (aq) + 2H_2O (l)$; $E_2^o = 1.21 \ V$
$MnO_4^- (aq) + 4H^+ (aq) + 3e^- \to MnO_2 (s) + 2H_2O (l)$; $E_3^o = ?$
Value of $E_3^o$ will be ............ $V$

If the $E^{0}$ values for $Mg^{+2} | Mg$,$Zn^{+2} | Zn$,and $Fe^{+2} | Fe$ are $-2.37 \ V$,$-0.76 \ V$,and $-0.44 \ V$ respectively,which statement is correct?

Calculate the standard cell potential $(E_{cell}^{o})$ for the following electrochemical cells:
$(i)$ $Al_{(s)}|Al_{(1M)}^{3+}||Cu_{(1M)}^{2+}|Cu_{(s)}$
$(ii)$ $Al_{(s)}|Al_{(1M)}^{3+}||Zn_{(1M)}^{2+}|Zn_{(s)}$
$(iii)$ $Al_{(s)}|Al_{(1M)}^{3+}||Ag_{(1M)}^{+}|Ag_{(s)}$
$($ Given: $E_{Al^{3+}|Al}^{o} = -1.66 \ V$,$E_{Zn^{2+}|Zn}^{o} = -0.76 \ V$,$E_{Cu^{2+}|Cu}^{o} = 0.34 \ V$,$E_{Ag^{+}|Ag}^{o} = 0.80 \ V$ $)$

For the feasibility of a redox reaction in a cell,the e.m.f. should be

$A$ galvanic cell consists of a copper electrode and a standard hydrogen electrode. If $E^\circ (Cu^{2+}_{(aq)} | Cu_{(s)}) = +0.34 \text{ V}$, identify the reaction taking place at the positive electrode during the working of the cell.

Ferrous ion $(Fe^{2+})$ can be oxidised by which of the following ions?