Question

What fraction of one edge centred octahedral void lies in one unit cell of fcc?

• A. $\frac 13$
• B. $\frac 14$
• C. $\frac {1}{12}$
• D. $\frac 12$

Answer 1

Answer: (B)

$\frac 14$

Answer 2

In a face-centered cubic unit cell, each edge is shared by 4 adjacent unit cells. Therefore, if you consider the edge-centered octahedral void, only $\frac 14^{th}$ of the void is contained within one unit cell. This is because each unit cell contributes $\frac 14^{th}$ of the void, and when you sum up the contributions from all adjacent cells, you get the complete void.

So, the correct option is (B): $\frac 14$