Chemistry - Solid State Question with Solution | TestHub

$\begin{array}{rl}& \because d=\frac{Z\times M}{N_A\times V}\\ & \therefore Z=\frac{d\times N_A\times V}{M}\end{array}$ As $a=5\mathring{A}=5\times 10^{-8}\mathrm{cm}\therefore V={\left(5\times 10^{-8}\right)}^3{\mathrm{cm}}^3$ Molecular mass, $M=56+16=72\mathrm{g}$ $\begin{array}{rl}Z& =\frac{4\times 6.023\times 10^{23}\times {\left(5\times 10^{-8}\right)}^3}{72}\\ & =4.16\approx 4\end{array}$ Four molecules of ferrous oxide, FeO per unit cell, it means that $4{\mathrm{Fe}}^{2+}$ and $4{\mathrm{O}}^{2-}$ ions are present in each unit cell.