The coordination number of an atom in a hexagonal close-packed $(hcp)$ structure is ...........

In an ionic crystal,$\frac{r^{+}}{r^{-}} = 0.524$,the coordination number of the cation is:

What is the value of the radius ratio for an ionic crystal having a coordination number of $6$?

What is the coordination number in a hexagonal close-packed $(h.c.p.)$ structure?

In a face-centered cubic $(FCC)$ lattice,$A$ atoms are present at the corners and $B$ atoms are present at the face centers. If one $B$ atom is removed from one of the face centers,what will be the molecular formula of the compound?

In a compound formed by $A^{+}$ and $B^{-}$ ions,$B^{-}$ ions are arranged at all corners except two and at all face centers except three,while $A^{+}$ ions are at the midpoints of all body diagonals. The molecular formula of the compound will be ................