The pyknometer density of NaCl crystal is `2.165xx10^(3)kg m^(-3)` while its X - rays density is `2.178xx10^(3)kg m^(-3)`. The fraction of the unoccupied sites in NaCl crystal is

Options

A. `5.968`
B. `5.96xx10^(-2)`
C. `5.96xx10^(-3)`
D. `5.96xx10^(-4)`

Answer

C

Explanation

Molar volume from pyknometer density `= (M)/(2.165xx10^(3))m^(3)`
Molar volume from X - ray density `= (M)/(2.178xx10^(3))m^(3)`
`therefore` Volume unoccupied `=((1)/(2.165)-(1)/(2.178))(M)/(10^(3))m^(3)`
Fraction unoccupied `=((1)/(2.165)-(1)/(2.178))//(1)/(2.165)`
`= 5.96xx10^(-3)`