Ionic conductance in solution depends upon the mobility of ions, which depend upon the degree (or extent) of hydration. Since charge/radius ratio is maximum for $\mathrm{L}{\mathrm{i}}^{+}$ , so it is hydrated to a maximum extent. Thus, the ionic size in aqueous solution, instead of increasing, actually decreases on moving from $\mathrm{L}{\mathrm{i}}^{+}$ to $\mathrm{C}{\mathrm{s}}^{+}$ .