In a closed vessel, every reaction below goes to completion. All gas volumes are measured at the same temperature and pressure, high enough for water to stay a vapour. Statement I: $30\ \text{mL}$ of hydrogen and $20\ \text{mL}$ of oxygen react to give $30\ \text{mL}$ of water vapour, and $5\ \text{mL}$ of oxygen is left. Statement II: $1.0\ \text{L}$ of oxygen, $\text{O}_2$, and $1.0\ \text{L}$ of ozone, $\text{O}_3$, contain the same number of oxygen atoms.