$\mathit{S}{\mathit{n}}_{\left(\mathit{a}\mathit{q}\right)}^{2+}+2\mathit{e}-\to \mathit{S}{\mathit{n}}_{\left(\mathit{s}\right)}$ $\mathit{E}\circ =-0.14\mathit{V}$ ____(i)
$2\mathit{f}{\mathit{e}}_{\left(\mathit{a}\mathit{q}\right)}^{+3}+2\mathit{e}-\to 2\mathit{f}{\mathit{e}}_{\left(\mathit{a}\mathit{q}\right)}^{+2}$ $\mathit{E}{\circ }_1=+0.77\mathit{V}$ ____(ii)
$\mathit{S}{\mathit{n}}_{\left(\mathit{s}\right)}\to \mathit{S}{\mathit{n}}_{\left(\mathit{a}\mathit{q}\right)}^{+2}+2\mathit{e}-$ $\mathit{E}{\circ }_2=0.14$ _____(iii)
On adding equation (ii) and (iii)
$2\mathit{F}{\mathit{e}}_{\left(\mathit{a}\mathit{q}\right)}^{+3}+\mathit{S}{\mathit{n}}_{\left(\mathit{s}\right)}\to 2\mathit{F}{\mathit{e}}_{\left(\mathit{a}\mathit{q}\right)}^{+2}+\mathit{S}{\mathit{n}}^{+2}$, $\mathit{E}\circ$
$-2\mathit{F}\mathit{E}\circ =2\mathit{F}\mathit{E}{\circ }_1+2\mathit{F}$ $\mathit{E}{\circ }_2$
$\mathit{E}\circ =0.77+0.14$
$\mathit{E}\circ =0.91\mathit{V}$
$\because \mathit{E}\circ >0$
∴ Sn is oxidised and the voltage at the cell is 0.91 V.