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 for calcium ion (Ca^(2+)) and fluoride ion (F^(-)) are-

'AB' has rock salt structure. Radius of cation is 100pm. If the radius of anion is 1.6 times that of cation then the edge length of unit cell "AB" will be

AB' has rock salt structure. Radius of cation is 100pm. If the radius of anion is 1.6 times that of cation then the edge length of unit cell "AB" will be