Here's why:

* Physical Properties: Describe a substance's appearance, texture, and how it behaves under different conditions (like temperature or pressure). They can be observed or measured without changing the substance's chemical composition. Examples include color, density, melting point, boiling point, and solubility.

* Chemical Properties: Describe how a substance reacts with other substances and changes its chemical composition. Examples include flammability, reactivity with acids, and oxidation.

Since the melting point of barium describes how it changes state (solid to liquid) without altering its chemical makeup, it's a physical property.