Answer
See the answer below.
Work Step by Step
The triple charged ions would require removing an electron from an inner shell for Mg and adding one to a new shell for O, in both cases breaking a noble gas electronic configuration (more stable) and is thus energetically unfavorable.
Measuring a property that increases with the strength of the ionic bond, like the melting point, and comparing it with other doubly ionic bonds, like CaO, and triply ionic ones, like AlP would work.
