The pyknometric density of sodium chloride crystal is $2.165 \times 10^3 kg\; m^{–3}$ while its X-ray density is $2.178 \times 10^3 kg \; m^{–3}$. The fraction of unoccupied sites in sodium chloride crystal is :

Question

( A ) $5.96 \times 10^{-1}$
( B ) $5.96 \times 10^{-2}$
( C ) $5.96$
( D ) $5.96 \times 10^{-3}$