Mg + O₂ → 2MgO

• Most metals burn to give basic oxides.
• Some dissolve in water to form alkaline solutions (which turn litmus blue).
• For example, MgO + H₂O → Mg(OH)₂ (slightly soluble); Na₂O + H₂O → 2NaOH.
• Non-metals. Coal (carbon) glows red and releases carbon dioxide:

C + O₂ → CO₂

• Most non-metals form acidic oxides, which dissolve in water giving acids (which turn litmus red).
• Examples: CO₂ + H₂O → H₂CO₃ (carbonic acid), S + O₂ → SO₂ and SO₂ + H₂O → H₂SO₃ (sulphurous acid).
• So metal oxides are usually basic; non-metal oxides are usually acidic.