Calculate the mass of 1 molecule of oxygen gas.
[Atomic mass of O = 16 u and NA = 6.022 x 1023 mol 1]
1 mole of oxygen molecules = 32 g of oxygen = 6.022 X ${10}^{23}$ molecules
6.022 X ${10}^{23}$ molecules of ${{O}{2}}$ weigh 32 g.
1 molecule of ${{O}{2}}$ weigh = 32 / 6.022 X ${10}^{23}$
= 5.313 x ${10}^{-23}$ g