Answer: 3 O2
Step-by-step explanation:
4AI +____O2 → 2Al₂O3.
In the product, Al and O3 are one chemical now and therefore BOTH impacted by the coeffcient in front of the Al which is 2. We know the coefficient is 2 and there are 3 molecules of O meaning that there are 6 molecules of O in the product. To balance this, there should be 6 molecules of O on the reactant side, the same way there is 4 Al molecules on both sides of the reaction. So 6 divided by 2 is 3 so put a 3 in the blank.