The reducing ability of the metals $K$,$Au$,$Zn$ and $Pb$ follows the order

Calculate $E^o_{cell}$ for the following cell in $V$:
$Zn_{(s)} | Zn^{2+}_{(aq.)} || Ag^{+}_{(aq.)} | Ag_{(s)}$
Given: $E^o_{Zn^{2+}/Zn} = -0.76 \ V$ ; $E^o_{Ag^{+}/Ag} = 0.80 \ V$

The reduction potential values are given below. Which is the strongest reducing agent? $Al^{3+}/Al = -1.67 \, V, Mg^{2+}/Mg = -2.34 \, V, Cu^{2+}/Cu = +0.34 \, V, I_2/2I^- = +0.53 \, V$

The standard reduction potential at $298 \ K$ for the following half-cell reactions is given as:
$Zn^{2+}_{(aq)} + 2e^{-} \rightarrow Zn_{(s)} ; \quad E^{\circ} = -0.762 \ V$
$Cr^{3+}_{(aq)} + 3e^{-} \rightarrow Cr_{(s)} ; \quad E^{\circ} = -0.740 \ V$
$2H^{+}_{(aq)} + 2e^{-} \rightarrow H_{2(g)} ; \quad E^{\circ} = 0.0 \ V$
$F_{2(g)} + 2e^{-} \rightarrow 2F^{-}_{(aq)} ; \quad E^{\circ} = 2.87 \ V$
Which of the following is the strongest reducing agent?

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

Why does copper not replace hydrogen from acids?