Answer
$75\%$ $Au,$ $25\%$ $Pd.$
Work Step by Step
1. One mole of atoms contains $ 6.022\times10^{23}$ atoms. Therefore
$\frac{2.49 \times 10^{23} }{6.022\times10^{23}} = 0.4135$ mole of atoms.
2. Now we compute number of moles of individual element using the following
1 mole of gold = 197.0 g
1 mole of palladium = 106.4 g
$mole Au + mole Pd = 0.4135 $
$mole Au\times 197 + mole Pd\times106.4 = 67.2$
Two equations in two unknowns, simplify them to get
mole Au =$0.2561$
mole Pd = $0.1574$
3. We need amount of Au, So grams Au = $0.2561 \times197 = 50.45 g $
4. Percentage conversion
$50.45 / 67.2 = 0.75 (75\% Au)$
