In a compound,atoms of element $Y$ form $ccp$ lattice and those of element $X$ occupy $2/3$ of tetrahedral voids. The formula of the compound will be

$A$ compound is formed by elements $A$ and $B$ which crystallizes in a $CCP$ structure. Atoms of $A$ are at the corners and atoms of $B$ are at the face centers. If two atoms of $A$ are missing from the unit cell,what is the molecular formula of the compound?

How will you distinguish between the following pairs of terms:
$(i)$ Hexagonal close-packing $(hcp)$ and cubic close-packing $(ccp)$?

In a mixed oxide of $A$ and $B$,$A$ occupies all the octahedral voids while $B$ occupies $(2/3)$rd of the tetrahedral voids. The molecular formula of this oxide is

What are $ABAB...$ packing and $ABCABC...$ packing respectively called?

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