Solve this:

Q.13. A solid has a bcc structure. If the distance of closest approach between the two atoms is 1.73$\stackrel{o}{A}$. The edge length of the cell is:
(A) 200 pm
(B) $\sqrt{3}/\sqrt{2}$ pm
(C) 142.2 pm
(D) $\sqrt{2}$ pm

 As the solid has bcc structure, the distance of nearest approach b/w two atoms would be equal to half the diagonal distance 

 i.e.              d= √3⁄2 a  

 d = distance between two atoms = 1.73 

  a = edge length 

 1.73=3√2a  

 Solving a will get edge length = 200pm so option A is correct