WAEC Chemistry 2015 Paper

Concept:Ionic oxides are formed when a metal reacts with oxygen to produce an ionic compound.Explanation:Classify each oxide according to the element combined with oxygen.Non-metals form covalent oxides because they share electrons with oxygen.$\mathrm{P}_4\mathrm{O}_{10}$ and $\mathrm{SO}_2$ are oxides of non-metals, phosphorus and sulfur, so they are covalent.$\mathrm{Al}_2\mathrm{O}_3$ is amphoteric, but aluminium has a high polarising effect, giving the oxide considerable covalent character.Magnesium is a strongly electropositive metal.In $\mathrm{MgO}$, magnesium forms $\mathrm{Mg}^{2+}$ ions and oxygen forms $\mathrm{O}^{2-}$ ions.These oppositely charged ions are held together by strong ionic bonds in a crystalline lattice.Hence, the ionic oxide listed is magnesium oxide.Answer:B. $\mathrm{MgO}$