Given :
Mass of gold ( Au ) is 212 gram.
To Find :
Atoms of gold present in 212 gram of gold.
Solution :
Molecular mass of gold is 197 gram.
So, number of moles of gold in 212 gram is :
[tex]n = \dfrac{212}{197} \ moles\\\\n = 1.076 \ moles[/tex]
Now, we know 1 mole of any element contains [tex]6.022 \times 10^{23}[/tex] atoms.
So, number of atoms present in 1.076 moles are :
[tex]N = 1.076 \times 6.022\times 10^{23}\\\\N = 6.48 \times 10^{23}[/tex]
Hence, this is the required solution.