Which of the following is least ionic?

If anion size increases then ionic character decreases , if cation size is Small then ionic character increases

Therefore, $\mathrm{Ionic} \mathrm{character} \mathrm{\alpha } \frac{\mathrm{cation} \mathrm{size}}{\mathrm{anion} \mathrm{size}}$

Here, for the given all compounds cation is same but anion is different

In ${\mathrm{CaI}}_2$, the anion ${\mathrm{I}}^{-}$has large in size . Hence, Among the given all compounds, ${\mathrm{CaI}}_2$ to be least ionic.