The vacant space in bcc lattice unit cell is:

Step 1: Packing efficiency of BCC unit cell - Packing efficiency of BCC unit cell is given by, \(\begin{aligned} & \text { Packing efficiency }=\frac{\text { Volume occupied by two spheres } \times 100}{\text { Volume of unit cell }} \\ & =\frac{2 \times \frac{4}{3} \pi r^3 \times 100}{a^3} \\ & =68 \% \end{aligned}\) - The \(\%\) volume occupied by atoms in a unit cell is \(68 \%\) Step 2: % Vacant space in BCC unit cell - % vacant space is given by, \(\begin{aligned} & \% \text { Vacant space }=100-\% \text { of the volume occupied by atoms } \\ & =100-68 \\ & =32 \% \end{aligned}\) - % Vacant space is \(32 \%\)