You are asked to balance the chemical equation H2 + O2 → H2O. How many of the following ways are the correct ways to balance this equation?

I. 2H2 + O2 → 2H2O

II. H2 + O2 → H2O

III. 4H2 + 2O2 → 4H2O

IV. H2 + 1/2O2 → H2O