Question

Calcium fluoride crystallizes in fluorite structure. The coordinates number for the cation and anion is respectively:

• A. $6,6$
• B. $6,4$
• C. $4,6$
• D. $8,4$

Answer 1

Answer: (D)

$8,4$

The $C{a}^{2+}$ ions are arranged in (ccp) arrangement, i.e. $C{a}^{2+}$ ions are present at all corners and tat the centre of each face of the cube. the fluoride ions occupy all the tetrahedral sites.

This is $8:4$ arrangement i.e., each $C{a}^{2+}$ ion is surrounded by $8F^{-}$ ions and each $F^{-}$ ion by four $C{a}^{2+}$ ions.