Which is an example of a gas?

Hydrogen is indeed an example of a gas. It is the lightest element on the periodic table and is commonly found in a gaseous state at room temperature and pressure. As a diatomic molecule (H₂), hydrogen is colorless, odorless, and tasteless, and it plays essential roles in various chemical reactions and processes, including combustion and the formation of water when it reacts with oxygen.

In contrast, the other choices represent substances that do not exist as gases under standard conditions. Calcium carbide is a solid compound commonly used in industrial applications. Acetone is a volatile liquid that can evaporate easily, but it is not classified as a gas. Gasoline is also a liquid fuel composed of hydrocarbons and does not exist as a gas at room temperature unless heated or significantly pressurized. Thus, among the options provided, hydrogen stands out as a representative of a gas.