It seems there is a misunderstanding in the question. Pyrite is an iron sulfide mineral with the chemical formula FeS2, and it does not contain copper Cu . To calculate the percentage composition by mass of iron Fe and sulfur S in pyrite, we will use the molar masses of these elements.The molar mass of iron Fe is 55.845 g/mol, and the molar mass of sulfur S is 32.066 g/mol. The molecular formula of pyrite is FeS2, so the molar mass of pyrite is:Molar mass of pyrite = Molar mass of Fe + 2 * Molar mass of SMolar mass of pyrite = 55.845 g/mol + 2 * 32.066 g/mol = 119.977 g/molNow, we can calculate the percentage composition by mass of iron Fe and sulfur S in pyrite:Percentage of Fe = Molar mass of Fe / Molar mass of pyrite * 100Percentage of Fe = 55.845 g/mol / 119.977 g/mol * 100 = 46.55%Percentage of S = 2 * Molar mass of S / Molar mass of pyrite * 100Percentage of S = 2 * 32.066 g/mol / 119.977 g/mol * 100 = 53.45%So, the percentage composition of iron Fe in pyrite is 46.55%, and the percentage composition of sulfur S is 53.45%. There is no copper Cu in pyrite.