Learning goal 1: A particular gas sample is made up of O2 molecules and H2 molecules. Identify what sort of substance it is.

The gas sample that consists of O2 (oxygen) and H2 (hydrogen) molecules is classified as a mixture. A mixture is a physical combination of two or more substances in which each substance retains its own chemical properties. In this case, the sample contains two distinct types of diatomic molecules: oxygen (O2), which is essential for respiration and combustion, and hydrogen (H2), which is a highly flammable gas.

Because these gases can be combined in various proportions without undergoing a chemical change, but rather retaining their individual characteristics, it can be determined that this gas sample is a mixture of gases, specifically a gas mixture. This is different from a compound, which would involve a chemical reaction leading to the formation of new substances.