What characteristic of carbon dioxide makes it denser than air?

The characteristic that makes carbon dioxide denser than air is its higher molecular weight. Carbon dioxide (CO2) has a molecular weight of approximately 44 g/mol, while the average molecular weight of air, which consists primarily of nitrogen (N2) and oxygen (O2), is around 29 g/mol. This difference in molecular weight means that for the same volume, carbon dioxide contains more mass than the air surrounding it.

A higher molecular weight means that carbon dioxide molecules are heavier than the average molecules in air, causing carbon dioxide to settle lower in the atmosphere and behave as a denser gas. This property of density is important in various contexts, such as in the behavior of gases in confined spaces and the dynamics of gases in the environment.

Characteristics such as being a non-metal or colorless have no direct relevance to its density. Similarly, while carbon dioxide is soluble in water, this property does not pertain directly to its density compared to air. Thus, the correct answer highlighting the molecular weight appropriately explains why carbon dioxide is denser than air.