Answer:
(b) 19.9 moles
Explanation:
To convert from moles Al to moles O₂, you need to multiply the given value by the mole-to-mole ratio of each component. This ratio is constructed via the coefficients in the balanced reaction. The desired unit (moles O₂) should be placed in the numerator to allow for the cancellation of units.
2 Al₂O₃ ----> 4 Al + 3 O₂
^ ^
26.5 moles Al 3 moles O₂
--------------------- x ---------------------- = 19.9 moles O₂
4 moles Al
