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

Formula used: Packing efficiency = packing fraction ×$\times$ 100

$\text{ Packing fraction }=\frac{Z\times \text{ volume occupied byatom in unit cell }}{\text{ Volume of unit cell }}$

Here, Z=4, therefore using the packing efficiency method, we will get its packing efficiency and then deduct it from 100 to determine the available space.

$\mathrm{CCP}=\frac{4{\times }^4/3\pi r^3}{(2\sqrt{2}r{)}^3}\times 100$

$= 0.74\times 100$

$= 74\%$

$\mathrm{vacant} \mathrm{space} = 100-74$ = 26 %

Z = 2 is the unit cell. Along with one in the cube's center, it has particles on each of its four corners. In order to find the empty space, we must first compute the packing efficiency of the object in question. Then, we must subtract this efficiency from 100.

$\text{ P.E. of }\mathrm{BCC}=\frac{2{\times }^4/3\pi r^3}{{\left(\frac{4r}{\sqrt{3}}\right)}^3}\times 100$

$= 0.68 \times 100$

$= 68\%$

$\mathrm{vacant} \mathrm{space} = 100-68 = 32 \%$

As a result, there is 26% and 32% of empty space in a body-centered packed structure and a cubic close packed structure, respectively.