In a AB unit cell (Rock salt type) assuming `A^(+)` forming fcc :

Options

A. The nearest neighbour of `A^+` is six `B^(-)` ion
B. The nearest neighbour of `B^(-)` is six `A^+` ion
C. The second neighbour of `A^+` is twelve `A^+`
D. The packing fraction of AB crystal is 0.79

Answer

ABCD

Explanation

Based on FCC crystal, like NaCl lattice
Packing fraction`=((4xx4/3pir_(A+)^3)+(4xx4/3pir_(B-)^3))/a^3=((4xx4/3pi a^3/(2sqrt2)^3)+(4xx4/3pi (a^3(0.414)^3)/(2sqrt2)^3))/a^3=0.79`