How many particles per unit cell are present in $BCC$ structure?

What is the coordination number of a particle in $hcp$ structure?

For tetrahedral coordination number,the radius ratio $\frac{r_{c^+}}{r_{a^-}}$ is

The $8:8$ type packing is present in which of the following?

The number of spheres contained $(i)$ in one body centred cubic unit cell and $(ii)$ in one face centred cubic unit cell,is

An oxide of $A$ crystallizes with $8$ atoms at the corners of the unit cell and $18$ oxygen atoms on the edges and on the faces symmetrically. What is the formula of this oxide?