In a hexagonal close packing $(hcp)$ lattice,each sphere touches ................... spheres in its own layer.

An ionic crystal $LiAg$ arranges in a cubic crystal system in which the coordination number of each $Li^+$ and $Ag^+$ is $8$. The crystal structure is:

$A$ cubic solid is made of two elements $P$ and $Q$. Atoms of $Q$ are at the corners of the cube and $P$ at the body-centre. What is the formula of the compound? What are the coordination numbers of $P$ and $Q$?

In the zinc blende structure,zinc atoms fill up:

The $FCC$ unit cell of a compound contains ions of $A$ at the corners and ions of $B$ at the centre of each face. What is the formula of the compound?

What is the coordination number of a cation in an ionic compound if the type of hole occupied by the cation is octahedral?