What is the total contribution of all corner particles in a $bcc$ unit cell?

$A$ compound is formed by cation $C$ and anion $A$. The anions form hexagonal close packed $(hcp)$ lattice and the cations occupy $75 \%$ of octahedral voids. The formula of the compound is

An ionic solid is $HCP$ of $B^{2-}$ ions and $A^{x+}$ ions are in one-fourth of tetrahedral voids. The value of $x$ should be

Which arrangement is most suitable for the uniform packing of atoms in a layer?

Packing fraction of a layer in $2D$ hexagonal close packing arrangement is:

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