Allotropes of an element differ in their

Allotropes of an element are different forms or structures of the same element in the same physical state. They differ in their physical properties, such as color, melting point, boiling point, and density, due to the variations in the arrangement of atoms or molecules. For example, diamond and graphite are allotropes of carbon, and they have different physical properties because of their different atomic arrangements. Although allotropes have different physical properties, they have the same chemical properties, as they are composed of the same element with the same number of protons and electrons. Therefore, the correct answer is "physical properties".