Consider the cell,
$P t \mid H_{2}(g, 1\, atm) H^{+}(a q, 1\, M) \| F e^{3+}(a q)$
$F e^{2+}(a q) \mid P t(s)$
Given that $E^{o}{ }_{F e^{3+} / F e^{2+}}=0.771\, V$, the ratio of concentration of $F e_{(a q)}^{2+}$ to $F e_{(a q)}^{3+}$ is,
when the cell potential is $0.830\, V$.