The number of octahedral voids per lattice site in a lattice is ______. (Rounded off to the nearest integer)

In a close-packed lattice (such as FCC or HCP), the number of octahedral voids per lattice site (i.e., per atom) is a well-known result in solid state chemistry.

For a face-centred cubic (FCC) lattice, the number of atoms per unit cell is 4. The octahedral voids are located at the body centre (1 void) and at the midpoints of each edge (12 edges, each shared among 4 unit cells, giving $$12 \times \frac{1}{4} = 3$$ voids). The total number of octahedral voids per unit cell is $$1 + 3 = 4$$.

The ratio of octahedral voids to lattice sites is $$\frac{4}{4} = 1$$.

Therefore, the number of octahedral voids per lattice site is $$1$$.