${\mathrm{BeF}}_2$ is soluble in water, whereas the fluorides of other alkaline earth metals are insoluble because of

Fluorides of alkaline earth metals except ${\mathrm{BeF}}_2$ are insoluble in water. The solubility of ${\mathrm{BeF}}_2$ in water is due to higher hydration energy on account of small size of ${\mathrm{Be}}^{2+}$ ion and ${\mathrm{F}}^{-}$ ion and high charge density of ${\mathrm{Be}}^{2+}$ ion.