How does an element's oxidation number affect the acidity of its oxide?

An element's oxidation number is a key factor in determining the acidity of its oxide: as the oxidation number of an element increases, the acidity of its oxide generally increases.1

This trend is clearly observed in transition metals. For example, among the various oxides of manganese, $\text{MnO}$ (where manganese is in a +2 state) is the least acidic, while ${\text{Mn}}_2{\text{O}}_7$ (containing ${\text{Mn}}^{7+}$) is the most acidic.1

The chemical behavior of these oxides is closely linked to their bonding nature:
* Lower oxidation states (+1, +2, +3): These typically form ionic compounds that behave as basic oxides, reacting with acids to form salts and water.1
* Intermediate oxidation states (+4): These are often amphoteric, meaning they can react as either acids or bases.1
* Higher oxidation states (+5, +6, +7): These form covalent compounds that are acidic, reacting with hydroxide solutions to produce salts and water.1