If the atomic mass of 1 oxygen atom is 15.9994 amu, how much mass does of oxygen have?

Oxygen being a gas having two atoms of oxygen then so it will have a mass of 30 amu. for each molecule.

Oxygen's atomic weight is 16.00 amu. 1 mole of oxygen is 6.02 x 1023 atoms of oxygen 1 amu = 1.661 x 10-24g What is the molar mass (g/mole) of oxygen? Molar mass (in grams) is always equal to the atomic weight of the atom! Molar mass (in grams) is always equal to the atomic weight of the atom!