Explanation: Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis. For example, sodium oxide $(\mathrm{Na}_2\mathrm{O})$ and potassium oxide $(\mathrm{K}_2\mathrm{O})$ dissolve in water to produce alkalis sodium hydroxide and potassium hydroxide respectively. The reactions can be represented as follows:$\mathrm{Na}_2\mathrm{O}(\mathrm{s}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\;\rightarrow 2\mathrm{NaOH}(\mathrm{aq})$$\mathrm{K}_2\mathrm{O}(\mathrm{s}) + \mathrm{H}_2\mathrm{O}(\mathrm{l})\;\rightarrow 2\mathrm{KOH}(\mathrm{aq})$