What is the standard electrode potential $(E^o)$ for the electrode represented by $Pt, O_2(1 \, atm) | 2H^+(1 \, M)$?

For the following cell,the standard potential of the copper electrode is $0.337 \ V$ and the standard cell potential is $0.463 \ V$ for the reaction $Cu|Cu^{2+}(1 \ M)||Ag^{+}(1 \ M)|Ag$. What is the standard potential of the silver electrode (in $V$)?

Consider the half-cell reduction reactions:
$Mn^{2+} + 2e^{-} \rightarrow Mn$,$E^{\circ} = -1.18 \ V$
$Mn^{3+} + e^{-} \rightarrow Mn^{2+}$,$E^{\circ} = +1.51 \ V$
The $E^{\circ}$ for the reaction $3Mn^{2+} \rightarrow Mn + 2Mn^{3+}$,and the possibility of the forward reaction are respectively:

What does the negative sign in the expression $E_{Zn^{2+}|Zn}^o = -0.76 \ V$ mean?

Electrode potential of the half cell $Hg(\ell) | Hg_2Cl_{2(s)} | Cl^-_{(aq)}$ can be increased by

Which one of the following metals cannot evolve $H_2$ from acids,$H_2O$,or from its compounds?