Percentages of free space in cubic close packed structure and in body centered packed structure are respectively

What is the full form of $fcc$?

$A$ metal crystallizes in a lattice having $AB AB AB$ sequence of layers. This arrangement of spheres corresponds to which type of packing,and what is the percentage of empty space (void volume) in this lattice?

In a crystalline solid,anion $B$ are arranged in $ccp$ lattice and cation $A$ occupy $50\%$ of the octahedral voids and $50\%$ of tetrahedral voids. What will be the formula of the crystalline solid?

Find the void volume of a $bcc$ unit cell in $cm^3$ if the volume of the unit cell is $1.5 \times 10^{-22} \ cm^3$.

$A$ metal crystallises in an $FCC$ lattice with $ABCABC...$ packing. If the distance between the nearest neighbours is '$a$',then the distance between the centres of the nearest triangular voids of two consecutive layers is: