Gold forms a substitutional solid solution with silver. Compute the weight percent of gold that must be added to silver to yield an alloy that contains 6.5 × 1021 Au atoms per cubic centimeter. The densities of pure Au and Ag are 19.32 and 10.49 g/cm3, respectively. Also, the atomic weights for gold and silver are 196.97 and 107.87 g/mol, respectively.