Which has a higher mass percent of magnesium mgo or mg3n2?

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

Ithink this is what you meant. the temperature at which a liquid begins to boil is called the boiling point. the boiling point of water is 212°f or 100°c.  and at that point will start to turn into steam (gas)