The first step to solve this question is to convert the given mass of copper to moles using its molecular mass (63.5g/mol):
[tex]12.8g\cdot\frac{1mol}{63.5g}=0.2mol[/tex]Now, use Avogadro's number to find the number of atoms in 0.2 moles. Remember that it states the number of atoms in 1 mole of substance is 6.022x10^23.
[tex]0.2mol\cdot\frac{6.022\times10^{23}atoms}{1mol}=1.2044\times10^{23}atoms[/tex]There are 1.2044x10^23 atoms of copper in 12.8g of copper metal.
