(i) BeO is almost insoluble in water as it is covalent in nature and tightly held together in the solid state while $\mathrm{BeSO_4}$ is highly soluble in water due to high energy of solvation of smaller $\mathrm{Be}^{2+}$ ion. (ii) The size of $\mathrm{O}^{2-}$ ion is much smaller than that of the $\mathrm{SO}_4^{2-}$ ion. Since a bigger anion stabilises a bigger cation more than a smaller anion therefore, the lattice energy of BaO is much smaller than that of $\mathrm{BaSO_4}$ and hence BaO is soluble while $\mathrm{BaSO_4}$ is insoluble in water. (iii) LiI having much more covalent character than KI because of small size of Li+ as compared to $\mathrm{K}^{+}$. Hence, LiI is more soluble in ethanol.