Need formula of magnesium nitride, an ionic compound.
Mg2+ and N3-
together make
Mg3N2
--------------
so
3 * 24.31 g = 72.93 grams
2 * 14.01 g = 28.02 grams
------------------------------------------add
= 100 .95 grams/mole
--------------------------------molar mass magnesium nitride