Question

An atom 'P' crystallises in bcc form. What would be the fraction of an edge of unit cell that is not covered by atoms?

• A. $0.134$
• B. $0.172$
• C. $0.268$
• D. $0.290$

Answer 1

The correct option is A $0.134$

Given that an atom P crystallises in a bcc lattice.

The edge not covered by atom $=a-2R$

For bcc, $R=$ $\frac{\sqrt{3}a}{4}$

So, the edge not covered $=a-\frac{\sqrt{3}a}{2}=a\left[\frac{2-\sqrt{3}}{2}\right]$

Fraction of an edge of unit cell not covered by atoms $=\frac{a\times \frac{2-\sqrt{3}}{2}}{a}$ $=0.134$