Sodium metal crystallizes in a body centred cubic lattice with a unit cell edge of 4.29 Å. The radius of sodium atom is approximately :

Explanation

In bcc arrangement of atoms: 4 r = `sqrt(3)`a atoms on body diagonal remain in contact.
`rArr " " r = (sqrt(3)a)/(4) = (sqrt(3) xx 4.29)/(4) = 1.86` Å