**What Is The Mass Number Of Oxygen**. We will understand why knowing oxygen’s molar mass is. Thus, 4 moles of oxygen gas (o2) would have a mass of 128 g.

Oxygen has an atomic number of 8 , and the mass number of an atom is the sum of its atomic number plus its neutron number. How do you find the mass number of oxygen? Therefore, the number of neutrons in oxygen is 8.