1. Write the unbalanced chemical equation:

Al + O₂ → Al₂O₃

2. Balance the equation:

* Aluminum (Al): There are 2 aluminum atoms on the product side and 1 on the reactant side. Multiply Al on the reactant side by 2.

* Oxygen (O): There are 3 oxygen atoms on the product side and 2 on the reactant side. Multiply O₂ on the reactant side by 3/2 (to get 3 oxygen atoms).

The balanced equation is:

4 Al + 3 O₂ → 2 Al₂O₃

3. Determine the sum of coefficients on the reactant side:

The coefficients for the reactants are 4 and 3.

4 + 3 = 7

Therefore, the sum of coefficients on the reactant side is 7.