Question

find the mass of 2 moles of oxygen

Answer 1

31.998g /ml is your answer of your questions 64 is your answer approximately

Answer 2

Since oxygen has an atomic mass of 16 g/mole, the molar mass of oxygengas (O2) is 2 x 16 g/mole = 32 g/mole. 

Since 1 mole of oxygen is equivalent to 32 g, 
2 mole of oxygen gas would be equivalent to
=(2 x 32) gm = 64 gm

Thus, 2 moles of oxygen gas (O2) would have a mass of 64 gm

hope it'll help you :)