Answer :
(1) The theoretical yield of product,
is, 1.257 grams.
(2) The percent yield of
is, 64.13 %
(3) If the percent yield is calculated to be over 100% then there might be some impurity present in the desired product.
Solution : Given,
Mass of Mg = 0.7542 g
Molar mass of Mg = 24 g/mole
Molar mass of MgO = 40 g/mole
First we have to calculate the moles of Mg.

Now we have to calculate the moles of 
The balanced chemical reaction is,

From the reaction, we conclude that
As, 2 mole of
react to give 2 mole of 
So, 0.03142 moles of
react to give 0.03142 moles of 
Now we have to calculate the mass of 


Theoretical yield of
= 1.257 g
Experimental yield of
= 0.8922 g
Now we have to calculate the percent yield of 


Therefore, the percent yield of
is, 70.97 %
If the percent yield is calculated to be over 100% then the product would be greater than 1.257 g which indicates that there might be some impurity present in the desired product.