Answer:
The answer to your question is: Letter D.
Explanation:
To have a balanced reaction, the number of elements in the reactants, must be equal to the number of elements in the products.
So, count the number of elements in each side.
__Al + __O2 → __Al2O3
reactants elements products
1 Al 2
2 O2 3
It's unbalanced
Write a coefficient 4 in Al 4 Al + 3O2 → 2Al2O3
3 in O2
2 in Al2O3
And count again the number of elements
reactants elements products
4 Al 4
6 O2 6
Now, the reaction is balanced
