this is the corrosion process. But the final product should be rust, Fe(OH)₃(s), not Fe(OH)₂(s).
First step - iron reacts with O₂(g) and H₂O(l) and gives Fe(OH)₂(s) as the product.
Second step - that Fe(OH)₂(s) again reacts with O₂(g) and H₂O(l) and produce rust which is Fe(OH)₃(s).
so the final balanced equation for the whole process is,
4Fe(s) + 3O₂(g) + 6H₂O(l) → 4Fe(OH)₃(s)
To happen the corrosion, it required both O₂(g) and H₂O(l). If one of them is not present, then the corrosion will not happen.
