Explanation

(d)
The $Ca^{2 +}\$ions are arranged in (ccp) arrangement, $ie,$ $Ca^{2}$ ions are present at all corners and the centre of each face of the cube. The fluoride ions occupy all the tetrahedral sites. This is 8 : 4 arrangement, $ie,\ Ca^{2 +}$ ion is surrounded by $8F^{-}$ ions and each $F^{-}$ ion by four $Ca^{2 +}$ ions