When a 14.2-g sample of mercury (II) oxide is decomposed into its elements by heating, 13.2 g Hg is obtained. What is the percent composition of the compound?

Mercury (ii) oxide is made up of mercury and oxygen. The total mass of mercury (ii) oxide is 14.2 g, after decomposition 13.2 g of mercury were formed, therefore the mass of oxygen 1 g (14.2 g - 13.2 g).

Percentage of oxygen = (1/14.2) * 100 = 7.04%

Percentage of mercury = (13.2/14.2) * 100 = 92.96%

Therefore, percentage composition of the compound, oxygen is 7.04% and mercury is 92.96%.