When the equation ${\mathrm{Sn}}^{2+}\left(aq\right)+{\mathrm{IO}}_3^{-}\left(aq\right)+{\mathrm{H}}^{+}\left(aq\right)$ $⟶{\mathrm{Sn}}^{4+}\left(aq\right)+{\mathrm{I}}_2\left(aq\right)+{\mathrm{H}}_2\mathrm{O}\left(l\right)$ is balanced. what is the ${\mathrm{Sn}}^{2+}\left(aq\right)/{\mathrm{IO}}_3^{-}\left(aq\right)$ mole ratio?

When the reaction is balanced with smallest whole number then it can be given as,

$5{\mathrm{Sn}}^{2+}+2{\mathrm{IO}}_3^{-}+12{\mathrm{H}}^{+}⟶5{\mathrm{Sn}}^{4+}+{\mathrm{I}}_2+6{\mathrm{H}}_2\mathrm{O}$

Here, mole ratio of ${\mathrm{Sn}}^{2+}\left(aq\right)/{\mathrm{IO}}_3^{-}\left(aq\right)$ is 5/2.