$A$ metal oxide crystallises in a hexagonal close-packed $(HCP)$ array of oxide ions with two out of every three octahedral holes occupied by metal ions. The formula of the metal oxide is:

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:

What is the full form of $fcc$?

The total number of voids (octahedral + tetrahedral) in $1$ mole of a compound forming a hexagonal close-packed $(HCP)$ structure is:

Which of the following crystal lattice will have a void fraction of $0.476$?

Which one of the following statements about packing in solids is incorrect?