Here's why:

* Magnesium (Mg) is a metal, and its ionic form is Mg²⁺.

* Arsenic (As) is a nonmetal, and its ionic form is As³⁻.

* To balance the charges, we need three magnesium ions (3 x +2 = +6) and two arsenide ions (2 x -3 = -6).

* Therefore, the compound is Magnesium Arsenide.