Which of the following represents the hexagonal close-packed $(HCP)$ arrangement of spheres?

In a compound $XY$,the atoms of element $Y$ form a $ccp$ structure,while the atoms of element $X$ occupy $2/3$ of the tetrahedral voids. The molecular formula of the compound will be ..........

What is the percentage of empty space in a $bcc$ unit cell (in $\%$)?

Show that in a cubic close packed $(ccp)$ structure,eight tetrahedral voids are present per unit cell.

In an $fcc$ arrangement of $A$ and $B$ atoms, $A$ atoms are at the corners of the unit cell and $B$ atoms are at the face centers. If one of the $A$ atoms is missing from one corner, what is the simplest formula of the compound?

The close packing that represents the $ABC ABC......$ order is: