Li forms BCC structure. The edge length is 351 pm. Metallic radius of Li is ___ ?

In a BCC, in addition to the corners of a cube, an atom is placed at its centre. They touch each other by the body diagonal.

Therefore, 

$$\begin{gathered} \sqrt{3} a = 4 r^{+} \\ {r}^{+} = 151.987 pm \end{gathered}$$