pts$)1.$ In one unit cell of a crystal material made of the same type atoms, assume that all atoms contact closely to each other, calculate the number of atoms per unit volume for:

$($a$)$ BCC structure, as shown in Figure $1($a$)$;

$($b$)$ FCC structure, as shown in Figure $1($b$).$

Figure $1.$ Unit cells for $($a$)$ BCC and $($b$)$ FCC structures with atoms closely contact each other.