Which one of the following will increase the voltage of the cell? 

$\mathrm{Sn}\left(\mathrm{s}\right)+2{\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)\to {\mathrm{Sn}}^{2+}\left(\mathrm{aq}\right)+2\mathrm{Ag}\left(\mathrm{s}\right)$

${\mathrm{E}}_{\mathrm{cell}}={\mathrm{E}}_{\mathrm{cell}}^{\mathrm{o}} - \frac{2.303\mathrm{RT}}{\mathrm{nF}}\log \frac{\left[{\mathrm{Sn}}^{2+}\right]}{{\left[{\mathrm{Ag}}^{+}\right]}^2}$.

 Increase in the concentration of ${\mathrm{Ag}}^{+}$ decreases the value of $\log \frac{\left[{\mathrm{Sn}}^{2+}\right]}{{\left[{\mathrm{Ag}}^{+}\right]}^2}$.

This results in the increased value of ${\mathrm{E}}_{\mathrm{cell}}$