Which metal does not give the following reaction? $M + \text{water} \rightarrow \text{oxide or hydroxide} + H_2$

On the basis of the following electrode potentials,which one is the strongest reducing agent?
$E^0_{Cr_2O_7^{2-}/Cr^{3+}} = 1.33 \text{ V}$,$E^0_{MnO_4^-/Mn^{2+}} = 1.51 \text{ V}$,$E^0_{Br_2/Br^{-}} = 1.09 \text{ V}$,$E^0_{Zn^{2+}/Zn} = -0.76 \text{ V}$

Given at $298 \ K$: $E^\ominus_{Fe^{2+}/Fe} = X \ V$; $E^\ominus_{Fe^{3+}/Fe} = Y \ V$. The $E^\ominus_{Fe^{3+}/Fe^{2+}}$ in Volt at $298 \ K$ is given by:

If standard reduction potentials $(E^0)$ of $(Al^{+3}(aq)|Al(s))$, $(Fe^{+2}(aq)|Fe(s))$, $(Cu^{+2}(aq)|Cu(s))$ and $(Ag^{+1}(aq)|Ag(s))$ are $-1.66 \text{ V}$, $-0.44 \text{ V}$, $+0.34 \text{ V}$ and $+0.79 \text{ V}$ respectively, which of the following reactions is non-spontaneous?

What is denoted by a negative $E^o$ and a positive $E^o$ value in electrochemistry?

The formal potential of $Fe^{3+}/Fe^{2+}$ in a sulphuric acid and phosphoric acid mixture $(E^{\circ}=+0.61 \ V)$ is much lower than the standard potential $(E^{\circ}=+0.77 \ V)$. This is due to