If the number of atoms in a unit cell is $2$,then the number of tetrahedral and octahedral voids will be ....... and ....... respectively.

In a cubic close packed structure,the fractional contributions of an atom at the corner and at the face in the unit cell are,respectively:

In a face-centred cubic lattice,atom $A$ occupies the corner positions and atom $B$ occupies the face-centred positions. If one atom of $B$ is missing from one of the face-centred points,the formula of the compound is

Give two examples of metals that crystallize in the $hcp$ (hexagonal close-packed) structure.

In a simple cubic lattice,what percentage of the space is left unoccupied by the spheres?

Fill in the blanks:
$(a)$ In $ccp$ structure,$a = \dots \dots r$.
$(b)$ In $hcp$ structure,packing efficiency $= \dots \dots \%$.
$(c)$ In $bcc$ structure,percentage of packing efficiency $= \dots \dots \%$.