Arrange the following metals in the order of their decreasing standard electrode potential: $Mg, K, Ba, Ca$.

The $E^o$ for half cells $Fe/Fe^{2+}$ and $Cu/Cu^{2+}$ are $-0.44 \, V$ and $+0.32 \, V$ respectively. Then

Which electrode is used to measure the electrode potential of any electrode?

What is the standard reduction potential $(E^o)$ for $Fe^{3+} \to Fe$ ? ............... $V$
Given that :
$Fe^{2+} + 2e^- \to Fe;$ $E^o_{Fe^{2+}/Fe} = -0.47 \ V$
$Fe^{3+} + e^- \to Fe^{2+};$ $E^o_{Fe^{3+}/Fe^{2+}} = +0.77 \ V$

On the basis of the following $E^o$ values,the strongest oxidizing agent is:
$[Fe(CN)_6]^{4-} \to [Fe(CN)_6]^{3-} + e^-; E^o = -0.35 \ V$
$Fe^{2+} \to Fe^{3+} + e^-; E^o = -0.77 \ V$

Which of the following metals will not release $H_{2(g)}$ upon reaction with an acid?