Which is an example of a solid?

Magnesium is classified as a solid at room temperature, which aligns perfectly with the definition of a solid: a state of matter characterized by its definite shape and volume. In contrast, gasoline, chlorine, and acetone are not solids at standard conditions. Gasoline is a liquid that comprises hydrocarbon compounds, while chlorine is typically encountered as a gas under normal temperatures. Acetone is also a liquid at room temperature, commonly used as a solvent. Thus, magnesium stands out as the only substance in the list that conforms to the characteristics of a solid.