4. What is the empirical formula of a compound that contains 12.1% C, 16.2% O, and 71.7% Cl?

A. COCl
B. COCl₂
C. C₂OCl
D. CO₂Cl
E. ClCO₄

5. Which of the following ores containing Cu (63.5 g/mol) has the highest percentage of Cu by mass? (The molar masses are given inside the parenthesis.)

A. Chalcopyrite, CuFeS₂ (183.5 g/mol)
B. Chalcocite, Cu₂S (159 g/mol)
C. Covellite, CuS (95.6 g/mol)
D. Cuprite, Cu₂O (143 g/mol)
E. Tenorite, CuO (79.5 g/mol)

6. An ore containing gold was processed so that all of the gold is converted to AuCl₃ (303 g/mol). If a 4.0 g sample of an ore produced 3.03 g of AuCl₃, what is the percentage of Au (197 g/mol) in the ore?

A. 10.0 %
B. 49.3 %
C. 75.8 %
D. 98.5 %
E. 24.6 %