A solid metal oxide ($M_2{O}_3$ ) crystallizes as HCP for $O^{2-}$ ions and the metal ions    ( $M^{3+}$) occupy only octahedral voids in ideal crystal. The metal may exhibit +3 and+4 oxidation states. The composition of a real metal oxide crystal is found to be ${\text{M}}_{0.\text{6}0}{\text{O}}_{\text{1}.00}$. The percentage of metal atoms missing in the crystal is x% and the ratio of numbers of  $M^{3+}$ and  $M^{4+}$ ions in the crystal is y:1