Which of the following chlorides will show the highest covalent character?

How would you explain the following observations?
$(i)$ $BeO$ is almost insoluble but $BeSO_4$ is soluble in water.
$(ii)$ $BaO$ is soluble but $BaSO_4$ is insoluble in water.
$(iii)$ $LiI$ is more soluble than $KI$ in ethanol.

Which of the following compounds is the least soluble in water?

Which is the correct decreasing order of polarizability of the following ions?

Which one of the following is the highest melting halide?

Which of the following diagrams shows the correct change in the ionic character of the given compounds according to Fajans' rule?