In two separate experiments, the same quantity of electricity was passed through silver and gold solutions. [Assume ' $l$ ' constant]. The amounts of Ag and Au deposited are 2.15 and 1.31 g , respectively. The valency of gold is

[atomic mass of $\mathrm{Ag}=107.9$; $\mathrm{Au}=197$ ]

Given, $E_{\mathrm{Mn}^{7+} / \mathrm{Mn}^{2+}}^{\circ}=1.51 \mathrm{~V}, E_{\mathrm{Mn}^{4+} / \mathrm{Mn}^{2+}}^{\circ}=1.23 \mathrm{~V}$ Calculate the $E_{\mathrm{Mn}^{7+} / \mathrm{Mn}^{4+}}^{\circ}$.

On passing a current of 1.2 A through a solution of salt of copper for $40 \mathrm{~min}, 0.96 \mathrm{~g}$ of copper was deposited. The equivalent weight of copper in g is

The electric charge for electrode deposition of one equivalent of a substance is equal to