Sodium metal crystallizes in B.C.C. lattice with edge length of 4.29A⁰. The radius of sodium atom is

In a body-centered cubic cell (bcc) (sphere along the body diagonal )

$$\begin{gathered} r = \frac{\sqrt{3}}{4}a \\ r = radius of sphere \\ a = edge lenght =4.29A^0 \\ \to r = \frac{\sqrt{3}}{4}x4.29 = 1.857A^0 \end{gathered}$$

Therefore, the correct option is D 1.857