How many moles of aluminum oxide would form if 12.5 moles of aluminum burned

Al + O2 - > Al2O3

Balance it:

2Al + 3O2 - > 2Al2O3

So you need 2 Al and 3 O2 to make 2 Al2O3 (aluminum oxide).

I'm going to assume you have all the O2 you need.

Since 2 mols of Al is needed to make 2 mols of the product, it's a 1:1 ratio. You get as much aluminum oxide for as much aluminum you burn.

So 12.5 mols if there is not a lack of the O2.