Magnesium bromide is an ionic compound, which when dissolved in water would completely ionize to give the magnesium and bromide ions as per the reaction,
[tex]MgBr_{2} (aq)---->Mg^{2+}(aq)+2Br^{-}(aq)[/tex]
Each unit of magnesium bromide gives one magnesium ion,[tex]Mg^{2+}[/tex] and two bromide ions, [tex]Br^{-}[/tex].
So a total of three ions(particles) would be liberated when one formula unit of magnesium bromide is dissolved in water.
