The densities of NaCl crystal as measured by Spectrometer and X - ray method are $2.165\times10^3 kgm^{-3}$ and $2.178\times10^3 kgm^{-3}$, respectively . The fraction of unoccupied sites in sodium chloride crystal is

Question

$(a)\;5.96\times10^{-3}\qquad(b)\;5.96\qquad(c)\;5.96\times10^{-2}\qquad(d)\;5.96\times10^{-1}$