Among the following which one has the highest cation of anion size ratio?

The size of cation is in order of$\mathrm{Li}^{+} < \mathrm{Na}^{+} < \mathrm{Cs}^{+}$ and the size of anions in the order of$\mathrm{I}^{-}>\mathrm{F}^{-}$ Thus, when the cation is largest and anion is smallest, the ratio of their sizes is maximum. Hence, cation to anion sizeratio is maximum for CsF.