Metal oxides that react with both acids and bases to produce salt and water are called:

Oxides are compounds formed when elements combine with oxygen. They are classified according to how they react with acids and bases:

Basic oxides: most metal oxides are basic. They react with acids to form salt and water. Examples: sodium oxide (Na2O), calcium oxide (CaO) and magnesium oxide (MgO). Soluble basic oxides, such as Na2O, dissolve in water to form alkalis.

Acidic oxides: most non-metal oxides are acidic. They react with bases to form salt and water, and many dissolve in water to form acids. Examples: carbon dioxide (CO2), sulphur dioxide (SO2), sulphur trioxide (SO3) and phosphorus pentoxide (P2O5).

Amphoteric oxides: these oxides show both acidic and basic properties. They react with acids as well as with bases to form salt and water. The word "amphoteric" comes from the Greek word "amphoteros", meaning "both".

Neutral oxides: these show neither acidic nor basic properties. Examples: carbon monoxide (CO), nitrous oxide (N2O), nitric oxide (NO) and water (H2O).

Common examples of amphoteric oxides are aluminium oxide (Al2O3) and zinc oxide (ZnO). Lead oxide and tin oxide are also amphoteric.

For example, aluminium oxide reacts:

• With hydrochloric acid (acting as a base): Al2O3 + 6HCl → 2AlCl3 + 3H2O.
• With sodium hydroxide (acting as an acid): Al2O3 + 2NaOH → 2NaAlO2 (sodium aluminate) + H2O.
• Similarly, zinc oxide reacts with hydrochloric acid to form zinc chloride, and with sodium hydroxide to form sodium zincate.
• This amphoteric nature of aluminium oxide is used in the Bayer process to extract pure alumina from bauxite ore, by dissolving it in sodium hydroxide.
• Water is also described as amphoteric (or amphiprotic), because it can act as both an acid and a base.

Why not the other options?

• ✗Basic oxides, such as CaO and Na2O, react only with acids.
• ✗Acidic oxides, such as CO2 and SO2, react only with bases.
• ✗Neutral oxides, such as CO and N2O, react with neither.