The non-stoichiometric compound, ${\mathrm{Fe}}_{0.94}\mathrm{O}$ is formed when $\mathrm{x}\%$ of ${\mathrm{Fe}}^{2+}$ ions are replaced, such that each ${\mathrm{Fe}}^{2+}$ ion is replaced by $2/3 {\mathrm{Fe}}^{3+}$ ions. $\mathrm{x}$ is

What type of crystal defect is indicated in the arrangement below? (Consider it a closed lattice where ${\mathrm{Na}}^{+} \text{and} {\mathrm{Cl}}^{-}$ are joined together and $\square$ represents a void)

$$\begin{gathered} {\mathrm{Na}}^{+}-{\mathrm{Cl}}^{-}-{\mathrm{Na}}^{+}-{\mathrm{Cl}}^{-} - {\mathrm{Na}}^{+}-{\mathrm{Cl}}^{-} \\ {\mathrm{Cl}}^{-}- \square - {\mathrm{Cl}}^{-}- {\mathrm{Na}}^{+ }- \square - {\mathrm{Na}}^{+} \\ {\mathrm{Na}}^{+}-{\mathrm{Cl}}^{-} -\square - {\mathrm{Cl}}^{-} - {\mathrm{Na}}^{+}-{\mathrm{Cl}}^{-} \\ {\mathrm{Cl}}^{-} - {\mathrm{Na}}^{+}- {\mathrm{Cl}}^{-}- {\mathrm{Na}}^{+}-\square - {\mathrm{Na}}^{+} \end{gathered}$$