In an atomic bcc, what fraction of edge is not covered by atoms ?

Edge not covered by atom = a – 2r also in
$\text{ bcc },4r=\sqrt{3}a\therefore$edge not covered =
$\mathrm{a}-\frac{\sqrt{3}}{2}\mathrm{a}=\mathrm{a}\left(\frac{2-\sqrt{3}}{2}\right)\Rightarrow$Fraction of edge
not covered by atoms 
$=\frac{2-\sqrt{3}}{2}=0.134$