what is the theoretical yield in grams of MgO if 2.54g Mg metal reacts with excess O2

Answer 1

2Mg + O2 ==> 2MgO

mols Mg = grams/atomic mass = ?
Convert mols Mg to mols MgO. Use 1 mol Mg = 1 mol MgO.
Now convert mols MgO to grams MgO. grams = mols x molar mass

Answer 2

82.9g