Manganese(VII) = Mn7+
Oxygen most often forms the oxide ion, O2-
Sulphate ion is represented by SO42-
Because the element magnesium is in the Group II category, it is has two electrons in its outer shell, donating them to leave it with a 2+ charge. Therefore, when it is in the ionized form, it is Mg2+
Barium ion = Ba2+Hydroxide ion = OH-