The compound that has higher mass percent is Mg3N2 which is 72%
explanation
calculate the % mass of Mg in each compound
% composition of mg= molar mass of Mg/ total molar mass of the compound x100
in MgO = 24 /40 x100 = 60%
in Mg3N2 =72/100 x100 = 72 %
therefore the % composition in Mg3N2 is higher
