The solution is here,
given mass of copper wire(m)=25 g
no. of moles in given mass of Cu=0.393
a) no. of atoms= no. of moles×avogardo's number
=0.393×6.023×10^23=2.36 ×10^23 atoms
b) 25 g of Cu wire has 0.393 moles
so 200 g of Cu wire has 0.393/25 × 200=3.144 mol.
no. of atoms= 3.144×2.023×10^23=1.89×10^24 atoms.
c) 25 g of Cu wire has 2.36×10^23 atoms
so 5 g of Cu wire has (2.36×10^23)/25 × 5
=4.72×10^22 atoms
( b can also be solve like c)
