The moles of Al that is needed to react with 6.34 moles of Fe3O4 is 16.9 moles
Explanation
8 Al+ 3Fe3O4 → 4 Al2O3 + 9Fe
use of mole ratio of Al: fe3O4 to calculate the moles of Al
The mole ratio of Fe3O4 : Al is 8:3 therefore the moles of Al =
6.34 moles x8/3 = 16.9 moles