# 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

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

Difference in density of NaCl crystal, in the two methods of measurement= $2.178\times10^3 - 2.165\times10^3 =0.013\times10^3$
Fraction of Vacant sites in the crystal = $\large\frac{0.013\times10^3}{2.178\times10^3}$$=5.96\times10^{-3}$
edited Mar 25, 2014