The packing efficiency in a body centered cubic $(bcc)$ structure is closest to $.... \, \%$

In a structure of mixed oxide,oxide ions are in $CCP$. One-fifth of tetrahedral voids are occupied by divalent ion $(A^{2+})$ while half of the octahedral voids are occupied by trivalent ion $(B^{3+})$. The formula of the oxide is:

Explain the calculation of packing efficiency in $hcp$ and $ccp$ structures with the help of a diagram.

In a face-centred cubic $(FCC)$ unit cell,what is the total volume occupied by the atoms?

When sodium is heated above $1000 \ K$,its crystal structure changes from $bcc$ to $fcc$. Assuming the metallic radius of the atom remains unchanged,the ratio of the fraction of volume occupied by atoms in $bcc$ and $fcc$ structures will be .......

The ratio of close-packed atoms to tetrahedral holes in cubic close packing is