The change in reduction potential of a hydrogen electrode from its standard value when the electrolyte solution contains $100 \mathrm{ml}$ of $1 \mathrm{M}$ $\mathrm{HCl}$mixed with $100 \mathrm{mL}$ of $1 \mathrm{M}$ $\mathrm{NaOH}$.

At $1 \mathrm{atm}$, a gas is bubbled through a solution that contains a mixture of $1 \mathrm{M} {\mathrm{Y}}^{-}$, $1 \mathrm{M} {\mathrm{X}}^{-}$, and $1 \mathrm{M} {\mathrm{Z}}^{-} \text{at} 25°\mathrm{C}$. If the reduction potential of $\mathrm{Z}>\mathrm{Y}>\mathrm{X},$ then:

Arrange the four metals $\mathrm{A},\mathrm{B},\mathrm{C}$ and $\mathrm{D}$ in the order of the decreasing ability to act as a reducing agent, based on the given information.

$\mathrm{I}.$ $\mathrm{A}, \mathrm{B} \& \mathrm{C}$ react with $1 \mathrm{M}$ $\mathrm{HCl}$ to give ${\mathrm{H}}_2$.

$\mathrm{II}.$ When $\mathrm{C}$ is added to the solutions of other metal ions, metal $\mathrm{B}$ and $\mathrm{D}$ are formed.

$\mathrm{III}.$ Metal $\mathrm{C}$ does not reduce ${\mathrm{A}}^{\mathrm{n}+}$.

$2{\mathrm{X}}^{-}+{\mathrm{Y}}_2\to 2{\mathrm{Y}}^{-}+{\mathrm{X}}_2$

$2{\mathrm{W}}^{-}+{\mathrm{Y}}_2\to$ no reaction

$2{\mathrm{Z}}^{-}+{\mathrm{X}}_2\to 2{\mathrm{X}}^{-}+{\mathrm{Z}}_2$

Which of the following statement is correct? 

$\mathrm{E}°$ here represents standard oxidation potential.

In the electrochemical cell,

$\mathrm{Mg}\left(\mathrm{s}\right)\left|{\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right)\Vert {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)\right|\mathrm{Zn}\left(\mathrm{s}\right); \mathrm{E}°=+3.13 \mathrm{V}$

The correct plot of ${\mathrm{E}}_{\text{cell }}$ versus $\log \frac{\left[{\mathrm{Mg}}^{2+}\right]}{\left[{\mathrm{Zn}}^{2+}\right]}$ will be represented as

In the electrochemical cell, $\mathrm{Mg}\left(\mathrm{s}\right) \left|{\mathrm{Mg}}^{2+}\left(\mathrm{aq}\right) \right|\left| {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right) \right|\mathrm{Zn}\left(\mathrm{s}\right); \mathrm{E}°=+3.13 \mathrm{V}$

The correct plot of ${\mathrm{E}}_{\text{cell }}$ versus $\log \frac{\left[{\mathrm{Mg}}^{2+}\right]}{\left[{\mathrm{Zn}}^{2+}\right]}$ will be represented as: