The correct option is C For an anion F− , number of nearest cations are 4
In fluorite structure, the Ca2+ forms the fcc lattice.
Thus, Ca2+ occupies the corners and face centres of the cube. F− ion occupies all the tetrahedral voids of the fcc.
Total CaF2 units in one unit cell =4
Nearest distance between two Ca2+ ions is the distance between corner and face centre which is equal to a√2
Option (a) is incorrect.
For a cation Ca2+, distance of the nearest anion is equal to the distance between Ca2+ ion present at corner and F− ion present at tetrahedral void, which is equal to √3a4
Option (b) is correct.
F− is present at tetrahedral voids, the number of nearest cations Ca2+ are 4
Option (c) is correct