Question 81: What fraction of one edge centred octahedral void lies in one unit cell of fcc?
(1) \frac{1}{4}
(2) \frac{1}{12}
(3) \frac{1}{2}
(4) \frac{1}{3}
Answer: Option (1)
Explanation:
In a face centred cubic (fcc) unit cell, octahedral voids are present at the centre of the unit cell
and at the centre of each edge.
An octahedral void located at the centre of an edge is shared equally by four adjacent unit cells.
Therefore, only one fourth of an edge centred octahedral void belongs to a single unit cell.
Hence, the fraction of one edge centred octahedral void present in one fcc unit cell is \frac{1}{4}.
Thus, the correct answer is option (1).