Which one of the following oxides is a neutral oxide?

Carbon monoxide (CO) is classified as a neutral oxide because it neither reacts with acids nor bases to form salts; it does not exhibit acidic or basic properties in aqueous solution. CO₂ is an acidic oxide (it reacts with water to form carbonic acid and with bases to form carbonates). Na₂O (sodium oxide) and MgO (magnesium oxide) are basic oxides as they are oxides of metals and react with acids to form salts and water. Other examples of neutral oxides include N₂O (nitrous oxide), NO (nitric oxide), and H₂O.