If the distance between Nat and C ions in sodium  chloride crystal is Xpm, the length of the edge of the unit cell is

Options

A. 4 X pm
B. X74 pm
C. `X//2` pm
D. 2Xpm

Answer

D

Explanation

This distance between sodium and chloride ions - X pm The distance between two chloride ions =`sqrt(X^(2)+X^(2))=sqrt(2X^(2))=Xsqrt2`
`p_(CI^(-))=(Xsqrt2)/(2)`
In a face-centred cubic lattice, anions touch each other along the face diagonal of the cube.
`a=(4r_(sigma))/sqrt(2)=(4Xsqrt2)/sqrt(2.2)=2X`