In the fluorite structure if the radius ratio is `(sqrt(3)/(2)-1)` how many ions does each cation touch?

In the fluorite structure the coordination number of Ca^(2+) ion is

In the Lewis structure for the selenite ion, SeO_(3)^(2-) , how many lone pairs are around the central atom?

In calcium fluoride, having the fluorite structure the coordination number of Ca^(2+) on and F^(-) ion are

In calcium fluoride, having the fluorite structure, the coordination number for calcium ion (Ca^(2+)) and fluoride ion (F^(-)) are-