Ionic bonds form always form between a metal and a nonmetal, so the answer is D, Magnesium and Bromine.
Sodium is a metal, so a bond between two Sodium atoms will not be ionic.
Fluorine is a non-metal, so a bond between two will be covalent bond instead of an Ionic.
Magnesium and Lithium are both metals, so a bond will not be ionic.
On the other hand, Magnesium is a metal and Bromine is a non-metal, so a bond between them will be ionic.
