# Oxides can be classified as acidic, basic, amphoteric or neutral. State the classification of each of the following oxides and, for each one, give a chemical reason to support your answer: sulfur dioxide (SO₂), calcium oxide (CaO), and carbon monoxide (CO).

> Cambridge International IGCSE Chemistry (0620) — 7.2 Oxides · State · 4 marks

## Mark scheme (4 marks)

1. Sulfur dioxide is an acidic oxide
2. Sulfur dioxide reacts with water to form an acid / reacts with bases or alkalis to form a salt and water (any one valid chemical reason)
3. Calcium oxide is a basic oxide
4. Carbon monoxide is a neutral oxide / does not react with acids or bases / does not form a salt

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