Question

The pyknometric density of sodium chloride crystal is `2.165xx10^(3)kg m^(-3)` while its `X` ray density is `2.178xx10^(3)kg m^(-3)` the fraction of unoccupied sites in `NaCl` crystal is
A. `5.96xx10^(-1)`
B. `5.96xx10^(-3)`
C. `5.96`
D. `5.96xx10^(-2)`

Answer 1

Correct Answer - 2
`X` ray density is higher because corresponds to occupied space only as `X`-rays are diffracted by constituet particles.On the hand ,pyknometric density is lower as it correspondense to occupied as well as unoccupied space. Thus, the fraction of unoccupied site in `NaCl` crystal is given as
`"X ray density -pyknometric density(u"/("X-ray density (occupied s")`
`=(2.178xx10^(3)-2.165xx10^(3))/(2.178xx10^(3))`
`=(0.013xx10^(3))/(2.178xx10^(3))`
`=0.00596=5.96xx10^(-3)`