Which of the following compounds is a neutral oxide?

Step 1: Analyze the question We need to identify which oxide is neutral, meaning it shows neither acidic nor basic properties. It does not react with water to form an acid or base, and it does not react with acids or alkalis to form salts.

Step 2: Explain the concept Oxides are classified as:

• Acidic oxides: oxides of non-metals that dissolve in water to form acids (e.g., CO₂, SO₂, SO₃).
• Basic oxides: oxides of metals (e.g., CaO, Na₂O).
• Amphoteric oxides: react with both acids and bases (e.g., ZnO, Al₂O₃).
• Neutral oxides: show no acidic or basic behavior. The common examples are CO, NO, N₂O and H₂O.

Step 3: Check each option

• A. Carbon (IV) oxide (CO₂): dissolves in water to form carbonic acid (H₂CO₃), so it is acidic.
• B. Sulphur (VI) oxide (SO₃): forms sulphuric acid (H₂SO₄), so it is strongly acidic.
• C. Sulphur (IV) oxide (SO₂): forms sulphurous acid (H₂SO₃), so it is acidic.
• D. Carbon (II) oxide (CO): does not react with water, acids or bases under normal conditions, so it is neutral.

Step 4: Answer The correct option is D. Carbon (II) oxide.

Tip: Remember the neutral oxides with the phrase "CO, NO, N₂O, and water are neutral." If the question asks about a neutral oxide and you see carbon (II) oxide (CO), it is almost always the answer. Also note that the Roman numeral tells you the oxidation state: carbon (IV) is CO₂, while carbon (II) is CO.