Sodium metal crystallizes in a body centered cubic lattice with the cell edge `a = 4.29 Å`. The radius of sodium atom is:

Explanation

In BCC structure
body diagonal `= 4 xx r_(Na) = sqrt3 xx a`
`4 xx r_(Na) = sqrt3 xx 4.29 rArr r_(Na) = (sqrt3)/(4) xx 4.29 = 1.86 Å`