* Oxygen is a gas at room temperature and pressure. It needs to be cooled significantly to become a liquid and then even further to become a solid.
* The "melting point" of oxygen is the temperature at which it transitions from a solid to a liquid. However, oxygen transitions directly from a gas to a solid (and vice-versa) at standard atmospheric pressure. This is called sublimation.
* The "triple point" of oxygen is the temperature and pressure at which all three phases (solid, liquid, and gas) coexist in equilibrium. For oxygen, this point is -218.79°C (-361.82°F) and 0.0015 atmospheres.
So, while oxygen doesn't have a traditional melting point, it does have a triple point.
