The correct option is
C In an unit cell, number of effective KCl molecules are 6
Edge length
=a=628pm
1st neighbour of
K+=Cl−=6 at a2=314 pm
6 first neighbours located at the distance of
a2. [For
K+ at body centre, these first neighbours are
6 Cl− present at faces.]
2nd neighbour of
K+=Cl−=12 at
a√2=628√2=444 pm
12 second neighbours located at the distance of
a√2[For
K+ at body centre, these second neighbours are
12 K+ present at the edges].
3rd neighbour of
K+=Cl−=8 at
√3a2=√3×6282=544 pm
8 Third neighbours located at the distance of
√3a2 [For
K+ at body centre, these third neighbours are
8 Cl− present at the corners].
In an unit cell, number of effective KCl molecules are 4.