[tex][tex]\begin{array}{lc}\text { Half reaction } & E^{\circ}(\mathrm{V}) \\ \mathrm{O}_2+4 \mathrm{H}^{+}+4 \mathrm{e}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O} & +0.815 \\ \mathrm{NAD}^{+}+\mathrm{H}^{+}+2 \mathrm{e}^{-} \rightarrow \mathrm{NADH} & -0.320\end{array}[/tex][/tex]
In human cells, a compound known as [tex]\mathrm{NADH}[/tex] is involved in a reaction that generates an electrical potential. The reaction is based on the two half reactions shown in the table above. The balanced equation for the overall reaction is shown below.
[tex]
\mathrm{O}_2+2 \mathrm{H}^{+}+2 \mathrm{NADH} \rightarrow 2 \mathrm{H}_2 \mathrm{O}+2 \mathrm{NAD}^{-}
[/tex]
a. How many moles of electrons are transferred for each mole of [tex]\mathrm{O}_2[/tex] that reacts? Justify your answer in terms of the balanced equation and the change in oxidation number of oxygen.