A sample of cinnabar, an ore containing mercury, weighs 681 grams. After smelting, it yields 587 grams of pure mercury. What is the percent composition of mercury in the ore?

86.2% of Hg in the ore

Explanation:

Percent composition is defined as one hundred times the ratio between mass of an element in a compound and total mass of the compound. Formula is:

% composition =  

If an ore weights 681g and contains 587g of mercury, percent composition is:

(587g Hg / 681g) × 100 = 86.2% of Hg in the ore