Which of the following metals does not liberate $\text{H}_2$ gas by reacting with $\text{HCl}$?

If standard reduction potential $(E^{\circ})$ of $(Mg^{2+}_{(aq)} \mid Mg_{(s)})$,$(Ag^{+}_{(aq)} \mid Ag_{(s)})$,$(Zn^{2+}_{(aq)} \mid Zn_{(s)})$ and $(Cu^{2+}_{(aq)} \mid Cu_{(s)})$ are $-2.37 \ V$,$+0.79 \ V$,$-0.76 \ V$ and $+0.34 \ V$ respectively. Which of the following reaction is spontaneous?

The reaction is spontaneous if the cell potential is

If $E^{\circ}_{Fe^{2+}/Fe} = -0.440 \ V$ and $E^{\circ}_{Fe^{3+}/Fe^{2+}} = 0.770 \ V$,then $E^{\circ}_{Fe^{3+}/Fe}$ is (in $V$)

Standard potential of electrode reaction $Cu^{2+}_{(aq)} + 2e^{-} \rightarrow Cu_{(s)}$ is $+0.34 \ V$. What is the standard potential of the reaction $2Cu_{(s)} \rightarrow 2Cu^{2+}_{(aq)} + 4e^{-}$?

When a $Zn$ piece is kept in a $CuSO_4$ solution,the copper gets precipitated because the standard reduction potential of zinc is