What will be the percent fraction of edge length not covered by atoms when a metal crystallises in bcc lattice?

For bcc, radius ,$\mathrm{r}=\frac{\sqrt{3}}{4}\mathrm{a}$
Edge length not covered by atoms $=\mathrm{a}-2\mathrm{r}$
$=\mathrm{a}-2\times \frac{\sqrt{3}}{4}\mathrm{a}=\mathrm{a}\left[\frac{2-\sqrt{3}}{2}\right]$
$\therefore$% of fraction not covered by atoms $=\frac{\mathrm{a}\left[{\displaystyle \frac{2-\sqrt{3}}{2}}\right]\times 100}{\mathrm{a}}=0.134\times 100=13.4\%$