Question 6
20 g of magnesium oxide contains 12 g of magnesium. What is the mass percentage of magnesium?
The right answer is the one marked above.
60%. The mass fraction is 12 g ÷ 20 g = 0.6, and a percentage is the fraction multiplied by 100.
Multiplying by 100 does not change the composition, only the units it is quoted in. For very small compositions the same figure is given as parts per million instead — the fraction times a million.