An alloy contains 97% by mass aluminium and 3% by mass
copper.
100 Kg of material containing copper =
100*(3/100)
                                                               Â
= 3 Kg of copper
moles of copper = mass/molarmass
                           Â
= 3000/63.55
                           Â
= 47.21 moles
1 mole of copper contains -----> 6.023*10^23 atoms of
copper
47.21 moles of copper contains ------>
(6.023*10^23*47.21)
                                                             Â
= 2.84*10^25 atoms of copper