In a crystalline solid anions $\mathrm{B}$ are arranged in cubic close packing. Cation $\mathrm{A}$ are equally distributed between octahedral and tetrahedral voids. If all the octahedral voids are occupied, the formula for the solid is

Consider the bcc unit cells of the solids $1$ and $2$ with the position of atoms as shown below. The radius of atom $\mathrm{B}\mathrm{ }$ is twice that of atom $\mathrm{A}.$ The unit cell edge length is $50\mathrm{ }\mathrm{\%}$ more in solid $2$ than in $1$ . What is the approximate packing efficiency in solid $2$ ?

An element crystallises in a face–centred cubic (fcc) unit cell with cell edge a. The distance between the centres of two nearest octahedral voids in the crystal lattice is:

The vacant space in bcc lattice unit cell is:

The packing efficiency of the face centered cubic (FCC), body centered cubic (BCC) and simple/primitive cubic (PC) lattices follows the order