In the $fcc$ structure, the number of tetrahedral holes per sphere is

$A$ solid is made of two elements $X$ and $Y$. Atoms of $X$ are in $FCC$ arrangement and $Y$ atoms occupy all tetrahedral sites. What is the possible formula of the compound?

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 elements has an $hcp$ structure?

Fill in the blanks:
$(a)$ In $ccp$ structure,$a = \dots \dots r$.
$(b)$ In $hcp$ structure,packing efficiency $= \dots \dots \%$.
$(c)$ In $bcc$ structure,percentage of packing efficiency $= \dots \dots \%$.

Calculate the total volume occupied by all particles in a $fcc$ unit cell if the volume of unit cell is $5.2 \times 10^{-23} \ cm^3$.