A) 6, 6
B) 8, 4
C) 4, 4
D) 4, 8
Correct Answer: B
Solution :
In\[\text{Ca}{{\text{F}}_{\text{2}}}\text{,}\]the\[\text{C}{{\text{a}}^{2+}}\]ions are arranged in ccp arrangement \[ie,\]\[\text{C}{{\text{a}}^{2+}}\]ions are present at all the corners and at the centre of each face of the cube. The fluoride ions occupy all the tetrahedral sites. In the \[\text{Ca}{{\text{F}}_{\text{2}}}\]structure, each \[{{\text{F}}^{-}}\]ion is surrounded by four \[\text{C}{{\text{a}}^{\text{2+}}}\]ions while each \[\text{C}{{\text{a}}^{\text{2+}}}\]ion is surrounded by eight\[{{\text{F}}^{-}}\]ions. Hence, the co-ordination numbers of \[\text{C}{{\text{a}}^{\text{2+}}}\]and \[{{\text{F}}^{-}}\]ions are 8:4.
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