What is standard electrode potential?

The values of $E^0$ for metals $A$,$B$,and $C$ are $0.34 \ V$,$-0.80 \ V$,and $-0.46 \ V$ respectively. State the correct order for their ability to act as reducing agents.

Which of the following transformations can be carried out by using $HI$ as a reducing agent,under acidic conditions?
[Given: $I_{2(s)} \rightarrow 2I^- ; E^{\circ} = 0.54 \ V$]
$(i)$ $Cu^+ \rightarrow Cu_{(s)} ; E^{\circ} = 0.52 \ V$
$(ii)$ $Cr^{3+} \rightarrow Cr^{2+} ; E^{\circ} = -0.41 \ V$
$(iii)$ $Fe^{3+} \rightarrow Fe^{2+} ; E^{\circ} = 0.77 \ V$
$(iv)$ $Fe^{2+} \rightarrow Fe_{(s)} ; E^{\circ} = -0.44 \ V$

$A$ $1.0 \ M$ solution with respect to each of the metal halides $AX_3, BX_2, CX_3$ and $DX_2$ is electrolysed using platinum electrodes. If
$E^o_{A^{3+}/A} = 1.50 \ V, \quad E^o_{B^{2+}/B} = 0.3 \ V,$
$E^o_{C^{3+}/C} = -0.74 \ V, \quad E^o_{D^{2+}/D} = -2.37 \ V.$
The correct sequence in which the various metals are deposited at the cathode is

Match the following:

List-$I$	List-$II$
$(A)$ Potential of hydrogen electrode at $pH = 10$	$(I)$ $0.76 \ V$
$(B)$ $Cu^{2+} | Cu$	$(II)$ $0.059$
$(C)$ $Zn | Zn^{2+}$	$(III)$ $-0.591 \ V$
$(D)$ $\frac{2.303 RT}{F}$	$(IV)$ $0.337 \ V$
	$(V)$ $-0.76 \ V$

$A$ $B$ $C$ $D$
$(a)$ $(III)$ $(I)$ $(II)$ $(V)$
$(b)$ $(II)$ $(V)$ $(I)$ $(IV)$
$(c)$ $(III)$ $(IV)$ $(I)$ $(II)$
$(d)$ $(V)$ $(I)$ $(IV)$ $(II)$

$A$ gas $X$ at $1 \, atm$ is bubbled through a solution containing a mixture of $1 \, M \, Y^{-}$ and $1 \, M \, Z^{-}$ at $25 \, ^oC$. If the reduction potential of $Z > Y > X$,then