Atoms of element $X$ form $hcp$ lattice and those of element $Y$ occupy $\frac{2}{3}$ of its tetrahedral voids. The percentage of element $X$ in the lattice is ..... . (Nearest integer)

What is the full form of $fcc$?

In the spinel structure,oxide ions are cubical-closest packed where $1/8$ of tetrahedral voids are occupied by $A^{2+}$ cations and $1/2$ of octahedral voids are occupied by $B^{3+}$ cations. The general formula of the compound having spinel structure is

The radius ratio of cation to anion for a triangular void is ....

Element '$B$' forms $ccp$ structure and '$A$' occupies half of the octahedral voids,while oxygen atoms occupy all the tetrahedral voids. The structure of bimetallic oxide is

With the help of a labelled diagram,show that there are $4$ octahedral voids per unit cell in a cubic close-packed $(CCP)$ structure.