Which one of the following oxides reacts with both acid and base?
Aluminium oxide
Calcium oxide
Sodium oxide
Potassium oxide
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UPSC CAPF – 2022
Amphoteric oxides are oxides that exhibit both acidic and basic properties, meaning they can react with both acids and bases to form salts and water.
Aluminium oxide (Al₂O₃) is a common example of an amphoteric oxide.
It reacts with acids: Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l)
It reacts with bases: Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2Na[Al(OH)₄](aq) (Sodium tetrahydroxoaluminate, also written as 2NaAlO₂ + 4H₂O or similar)
Calcium oxide (CaO), Sodium oxide (Na₂O), and Potassium oxide (K₂O) are typically basic oxides, reacting with acids but not bases (except perhaps very strong, concentrated bases in specific conditions not characteristic of amphoterism).