Which of the following is an example of a physical property?

• A. Ductility
• B. Flammability
• C. Toxicity
• D. Luster

Answer: (D)

A physical property is something you can observe or measure about a material without changing its chemical identity. Luster fits this idea because it describes how a surface reflects light. You can tell whether something has a shiny or dull surface just by looking at it, without causing any chemical change to the material.

The other choices involve chemical behavior rather than just how the material appears. Flammability describes whether a substance will burn in air, which is a chemical reaction and thus a chemical property. Toxicity refers to harmful biological effects that arise from chemical interactions, another chemical property. Ductility describes how a material deforms under tensile stress, which is a mechanical property about deformation under force rather than how the material interacts with light.