First, we must know Avogadro's number:
1 mol of any substance = 6.02x10^23 formula units (ions, atoms, molecules, etc)
Also, we can say this:
1 mol of Li2O = its mass expressed in grams
(from Li2O molar mass = 30 g/mol approx.)
Now,
1 mol Li2O = 30 g = 6.02x10^23 molecules Li2O
30 g Li2O ----------- 6.02x10^23 molecules Li2O
x ----------- 2.8x10^24 molecules Li2O
x = 140 g approximately
Answer: 140 g
