If $AB$ crystallizes in a zinc blende structure with $B^{-}$ ions at lattice points,what fraction of tetrahedral voids is occupied by $A^{+}$ ions? ............... $\%$

$A$ solid element (metal) crystallises in $ABABAB$ type packing in three dimensions. If the density of the element and its atomic radius are $5.0 \ g/cm^3$ and $100\sqrt{2} \ pm$ respectively, the atomic mass of the element is $(N_A = 6 \times 10^{23} \ mol^{-1})$

Atom $(A)$ is present in $ccp$ form,atom $(B)$ is present in all the octahedral voids,and atom $(C)$ is present in all the tetrahedral voids. If all particles touching one of the body diagonal axes are removed,find the empirical formula of the solid.

In a compound,atoms of element $Y$ form a $ccp$ lattice and atoms of element $X$ occupy $2/3$ of the tetrahedral voids. What is the formula of the compound?

What is the packing efficiency of $fcc$ crystal structure (in $\%$)?

In a face-centred cubic $(FCC)$ unit cell,what is the total volume occupied by the atoms?