Solubility depends on two factors:
Breaking of bonds to form ionic entities
The energy of solvation (hydration energy) of the entities through ionic interactions.
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Actinides
Lanthanides
F Block Elements
Covalent compounds like beryllium sulphate have a higher enthalpy of dissociation than ionic barium sulphate. But the smaller entities like beryllium have higher charge density, resulting in higher solvation, and hence, the release of hydration enthalpy is larger than the dissociating energy.
So, BeSO4 is more soluble than ionic BaSO4.