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

For a simple cubic $(SC)$,body-centered cubic $(BCC)$,and face-centered cubic $(FCC)$ unit cell with edge length $a$,what is the ratio of the radii of the atoms present in them?

In a crystal lattice,the number of octahedral voids compared to tetrahedral voids is ...............

$A$ compound formed by $Mg$,$Al$,and $O$ is found to have a cubic close-packed $(CCP)$ array of oxide ions,in which $Mg^{2+}$ ions occupy $\frac{1}{8}^{th}$ of the tetrahedral voids and $Al^{3+}$ ions occupy $\frac{1}{2}$ of the octahedral voids. The formula for the compound is:

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

Calculate the total volume of a simple cubic unit cell in $\text{cm}^3$ if the void volume is $2.0 \times 10^{-23} \text{cm}^3$.