I’m not sure if this is what you are looking for...
Fe + 3O2 --> 2Fe2O3 you can count. Here is how.
I see 4 Fe on the left side. I see 2 x 2 = 4 Fe on the right side.
I see 3 x 2 = 6 O atoms on the left side. I see 2 x 3 = 6 O atoms on the right side. Of course it's balanced.
