Which gas is produced in a reaction between hydrogen and oxygen?

In a reaction between hydrogen and oxygen, the primary products are water molecules. When hydrogen gas (H₂) reacts with oxygen gas (O₂) in a combustion reaction, the chemical equation can be represented as:

2 H₂ + O₂ → 2 H₂O

This reaction produces water in the form of water vapor when the temperatures are high enough, such as in combustion scenarios. Water is the molecule formed because each hydrogen atom combines with an oxygen atom to create the H₂O product.

Understanding this reaction is crucial since it not only illustrates the basic principles of chemical reactions but also emphasizes the formation of compounds through elemental interactions. The other options listed do not form as a result of this reaction, as nitrogen is not involved, ozone forms in different reactions typically involving electrical discharge, and carbon monoxide arises from incomplete combustion of hydrocarbons and not from the direct reaction of hydrogen and oxygen.