1 mole of NaCl=58.5 g =`6.02xx10^23` formula units.
`therefore` No. of formula units in 1 g of NaCl=`(6.02xx10^23)/58.5`
As one unit cell of NaCl contains 4 NaCl formula units, therefore, number of unit cells present in 1 g of NaCl =`(6.02xx10^23)/(58.5xx4)=2.57xx10^21`
