why sulphates of Mg and Be soluble in water?

Answers (1)
S sudhir

Hydration enthalpy is higher than that of lattice entalpy in Be and Mg sulphates. So they are soluble in water. 

Beryllium Sulfate is a white colored, crystalline, inorganic compound that emits toxic fumes of beryllium oxides and sulfur oxides upon heating. It is soluble in the water.

 The reaction between magnesium and dilute sulphuric acid to give lots of hydrogen and a colourless solution of magnesium sulphate. Notice that you get a solution, not a precipitate. The magnesium sulphate is obviously soluble.