Question

First order X-ray reflection ($\lambda$ = 154 pm) is maximum from a set of (2, 0, 0) planes of a B.C.C lattice was observed at ${16}^{\circ }$, 6’. Then, the edge length of unit cell is

• A. 360 pm
• B. 420 pm
• C. 560 pm
• D. 180 pm

Answer 1

The correct option is C

560 pm

For, first order reflection, n = 1
$\lambda =2dsin\theta ,d=\frac{\lambda }{2sin\theta }=\frac{154}{2\times 0.2773}=280pmd(2,0,0)=\frac{154}{\sqrt{2^2+0^2+0^2}}\Rightarrow a=2\times 280=560pm$