Chemistry - Solid State Question with Solution | TestHub

* FeO crystallizes in NaCl structure. ${\mathrm{Fe}}^{2+}$ occupies octahedral voids.

* Fe₀.₇₅O O²⁻ forms an FCC lattice.

* Assume 100-molecule crystal of Fe₀.₇₅O.

No. of Fe atoms = 75

No. of O²⁻ atoms = 100

By balancing the charge: $100\times 2=75Fe$

$x+y=75\dots (1)$

$2x+3y=200\dots (2)$

Solving these equations, we get:

$y=50$

$x=25$

* 100 molecules of Fe₀.₇₅O = 25 unit cells.

* 4 O²⁻ occupy 1 unit cell.

25 Fe²⁺ are present in 25 unit cells, so there is 1 Fe²⁺ per unit cell.