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

Question

Accepted Answer

B. 1. An **edge-centred octahedral void** sits at the **midpoint of an edge** of the unit cell. To find its contribution, we need to know how many unit cells share that edge.

2. Every **edge of a cube is shared among 4 neighbouring unit cells**, since 4 unit cells meet along any given edge in a crystal lattice.

3. Therefore, only a fraction of this void actually 'belongs' to one unit cell, and that fraction is found by dividing the whole void equally among the 4 sharing cells.

$$	ext{Contribution per unit cell} = \frac{1}{4}$$

Hence, the answer is **B**.