The possible molecular mass of MgSO₄ in its dilute solution can be 

MgSO₄ is an electrolyte in dilute solution it undergoes dissociation,accordingly molar mass changes. The range of molar mass is

$\frac{\mathrm{Normal} \mathrm{molar} \mathrm{mass}}{\mathrm{i}}$to Normal molar mass (i = Vant Hoff factor)

Molar mass is in between 60 and 120 for different degree of ionization in dilute solution