Among the listed gases, which one is the lightest?

Helium is the lightest gas among the options provided. When comparing the molecular weights of the gases listed, helium has an atomic mass of about 4 grams per mole. In contrast, nitrogen has an atomic mass of approximately 28 grams per mole, oxygen around 32 grams per mole, and carbon dioxide, which is composed of carbon and two oxygen atoms, has a molar mass of approximately 44 grams per mole.

The properties of gases are significantly influenced by their molecular weights; lighter gases rise in the atmosphere and have lower densities compared to heavier gases. Helium's lower molecular weight makes it much less dense than both the diatomic gases (nitrogen and oxygen) and carbon dioxide, which contributes to its use in balloons and as a lifting gas in various applications. This understanding of molecular weight is crucial in fields such as medicine and engineering, where the selection of gases is based on their physical properties and behaviors in different configurations.