Answer : The number of moles of
needed, 7.5 mole
Solution : Given,
Moles of Al = 5.0 moles
The balanced chemical reaction is,

From the balanced chemical reaction, we conclude that
As, 2 moles of Al react with 3 moles of

So, 5.0 moles of Al react with
moles of

Therefore, the number of moles of
needed, 7.5 mole