What is the result of combining a metal-oxide with H2O in chemical synthesis?

When a metal oxide reacts with water (H2O) during a chemical synthesis process, the result is typically a metal hydroxide. This reaction occurs because the metal oxide, which is typically a basic compound, will interact with water to produce a hydroxide ion (OH⁻) in solution. The general reaction can be represented as:

Metal oxide + Water → Metal hydroxide.

For example, when calcium oxide (CaO), a metal oxide, is combined with water, it forms calcium hydroxide (Ca(OH)₂). This process showcases the basic nature of metal oxides, as they often react with water to yield metal hydroxides, which are soluble in water and can dissociate into metal ions and hydroxide ions.

The other choices are less accurate in this context. Salt typically results from the neutralization of an acid and a base, which is not the scenario here. While metal oxide hydrate refers to a solid compound that includes water molecules, it does not directly reflect the outcome of the reaction with water. Hydrogen gas is not produced in this scenario, as the reaction does not involve the reduction of water or any hydrogen ions in this specific context. Consequently, the formation of metal hydroxide aligns precisely with the chemical reaction taking place