An alkaline earth metal 'M' readily forms water soluble sulphate and water insoluble hydroxide.

 Solubility of $\mathrm{BeSO}_{4}$ is highest among the given met sulphates

$\mathrm{BeSO}_{4}>\mathrm{MgSO}_{4}>\mathrm{CaSO}_{4}>\mathrm{SrSO}_{4}>\mathrm{BaSO}_{4}$

Solubility order for hydroxide is

$\mathrm{Be}(\mathrm{OH})_{2}<\mathrm{Mg}(\mathrm{OH})_{2}<\mathrm{Ca}(\mathrm{OH})_{2}<\mathrm{Sr}(\mathrm{OH})_{2}<\mathrm{Ba}(\mathrm{OH})_{2}$

Thus $\mathrm{BeSO}_{4}$ is soluble and $\mathrm{Be}(\mathrm{OH})_{2}$ is insoluble.

$\mathrm{BeO}$ does not form rock salt like structure.

In the solid state, it adopts the hexagonal neurtzite structure form while in the vapour phase, it is present as discrete diatomic covalent molecules.