A gold sample contains 90%` of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?

Explanation

Mass of pure gold in one gram of the sample =`(1xx90)/(100)=0.9g`
No. of moles of gold present`=("Mass of gold")/("Molar atomic mass")=((0.9g))/((0197"g mol"^(-1)))=0.046"mol"`
One mole of gold contains atoms=`N_(A)=6.022xx10^(23)`
0.046 mole of gold conatins atoms=`6.022xx10^(23)xx0.046=2.77xx10^(21)`