4 Na + O₂ = 2 Na₂O
4* 23 g Na --------> 16 g O₂
9.5 g Na ------------> ?
Mass of O₂ = 9.5 * 16 / 4 * 23
Mass = 152 / 92
Mass = 1.6521 g of O₂
Molar mass O₂ = 16.0 g/mol
1 mole O₂ ------------ 16.0 g
? mole O₂ ------------ 1.6521 g
mole O₂ = 1.6521 * 1 / 16.0
≈ 0.10325 moles of O₂
hope this helps!