JEE Main · 2015 · 04 Apr 2015 · Offline · s-Block Elements

Whether a sulphate dissolves comes down to a tug of war between lattice enthalpy, which holds the crystal together, and hydration enthalpy, which rewards dissolving. Hydration enthalpy tracks the cation's charge density, and $\mathrm{B}{\mathrm{e}}^{2+}$ -- the smallest alkaline-earth ion -- has by far the highest. For $\mathrm{BeS}{\mathrm{O}}_4$ that hydration enthalpy actually outweighs the lattice enthalpy, so it is the sulphate whose hydration energy exceeds its lattice energy; for the bigger $\mathrm{C}{\mathrm{a}}^{2+},\mathrm{S}{\mathrm{r}}^{2+}$ and $\mathrm{B}{\mathrm{a}}^{2+}$ the lattice side wins.