The unit cell of a $NaCl$ lattice:

The vacant space in the $bcc$ unit cell is .............. $\%$

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

In a face-centred cubic $(FCC)$ lattice,atoms of $A$ form the corner points and atoms of $B$ form the face-centred points. If two atoms of $A$ are missing from the corner points,the formula of the ionic compound is

$A$ compound $M_pX_q$ has a cubic close packing $(ccp)$ arrangement of $X$. Its unit cell structure is shown below. The empirical formula of the compound is:
$M = \square$
$X = \bigcirc$

In a face-centred cubic $(FCC)$ unit cell,what is the contribution of an atom located at the face to the unit cell?