NaCl has fcc structure, therefore we have 4 units of NaCl in one unit cell of NaCl. and 6.02×1023 units of NaCl=1mol =23+35.5=58.5g and molar mass of NaCl(23+35.5=58.5) =58.5g of NaCl permol =1mol=6.02×1023 units of NaCl ∵58.5g of NaCl contain =6.02×1023 units of NaCl ∴1g of NaCl contain =
6.02×1023
58.5
unit cells of NaCl =0.1029×1023 units of NaCl Also, ∵ Each unit cell contain 4 units of NaCl. ∴ Number of NaCl unit cells =0.0257×1023 unit cells of NaCl=2.5×1021 unit cells. Hence, option (d) is the correct answer.