What is the position of octahedral voids in FCC Unit cell?

The correct options are
B

body center

C

Edge center

Do you remember the 3D diagram we just saw?

Didn’t you see that there was an octahedral void right at the middle of the unit cell? This is the body center.

We also saw that there is an octahedral at each edge of the unit cell such that ${\frac{1}{4}}^{th}$ of the void is in one cell. From this we can conclude that there is one octahedral void located at the edge center of the unit cell.