Final answer:
The difference in the state of matter of mercury (a liquid) and gold (a solid) is an example of a d) physical property, which includes observable characteristics like melting point, without changing the substance's chemical identity.
Step-by-step explanation:
The difference in the state of matter of mercury and gold is an example of a physical property. Physical properties are characteristics that can be observed or measured without changing the substance's chemical identity. These include qualities such as color, melting point, boiling point, density, and electrical conductivity. Physical properties also involve the state of matter, so when speaking about mercury being a liquid at room temperature while gold is a solid, this difference is related to each element's melting point, which is a physical property. A physical change, on the other hand, is when a substance changes form, but not chemical composition, such as solid ice melting into liquid water.