Magnesium chloride dissolves in water to form:

hydrated  ${\mathrm{MgCl}}_2$ molecules

hydrated ${\mathrm{Mg}}^{2+}$ ions and hydrated ${\mathrm{Cl}}_2^{2-}$ ions

hydrated ${\mathrm{Mg}}^{2+}$ ions and hydrated ${\mathrm{Cl}}^{-}$ ions

hydrated Mg atoms and hydrated ${\mathrm{Cl}}_2$ molecules