Which of the following has a $4:2$ coordination number structure?

$A$ compound $M_pX_q$ has a cubic close packing $(ccp)$ arrangement of $X$. Its unit cell structure is shown below. The empirical formula of the compound is:
$M = \square$
$X = \bigcirc$

What is the total volume occupied by atoms in a face-centered cubic $(FCC)$ unit cell of a metal?

What is the total number of unit cells shared by each corner particle of a $bcc$ unit cell?

What is the total number of atoms in a $BCC$ crystal lattice having $1.8 \times 10^{20}$ unit cells?

Potassium fluoride $(KF)$ has an $NaCl$ type structure. What is the distance between $K^{+}$ and $F^{-}$ ions if the unit cell edge length is $a \ cm$?