$-{\mathrm{ClO}}_3^{-}+\dots {\mathrm{I}}^{-}+{\mathrm{H}}^{+}⟶-{\mathrm{Cl}}^{-}+\dots {\mathrm{I}}_2+{\mathrm{H}}_2\mathrm{O}$ 

When this equation is balanced with whole number coefficients, what is the ${\mathrm{H}}^{+}/{\mathrm{I}}_2$ coefficient ratio?

The complete reaction can be balanced as,

${\mathrm{ClO}}_3^{-}+6{\mathrm{I}}^{-}+6{\mathrm{H}}^{+}⟶{\mathrm{Cl}}^{-}+3{\mathrm{I}}_2+3{\mathrm{H}}_2\mathrm{O}$

The ${\mathrm{H}}^{+}/{\mathrm{I}}_2$ coefficient ratio is 2:1. Thus, option A is correct.