The equation that correctly balances Fe + O2 → Fe2O3 is as follows:

4Fe + 3O2 → 2Fe2O3

In this equation:

- Four iron (Fe) atoms react with three oxygen (O2) molecules.

- As a result, two iron(III) oxide (Fe2O3) molecules are formed.

This equation ensures that the law of conservation of mass is upheld, as the total number of atoms of each element remains the same on both sides of the equation.