A2.0 l volume of hydrogen gas is combined with 1.0 l of oxygen gas to produce 2.0 l of water vapor. does oxygen undergo a chemical or physical change? explain

The properties like shape, structure, etc. that define the appearance of matter is said to be its physical properties whereas the properties like oxidation, toxicity, etc. that defines how a new product is formed from the other substances is said to be its chemical properties.

It is given that a 2.0 L volume of hydrogen gas is combined with 1.0 L of oxygen gas to produce 2.0 L of water vapor.  The chemical reaction is as:

Since, the reaction between hydrogen and oxygen results in the formation of  complete new product, water. So, oxygen will undergo a chemical change.