Here's why:

* Viscosity: This is the resistance of a fluid to flow. A borax solution will have a different viscosity depending on its concentration. Higher concentrations of borax will result in a thicker, more viscous solution.

* Physical Property: Viscosity is a physical property because it can be observed and measured without changing the chemical composition of the borax solution.

Other physical properties of a borax solution include:

* Color: A borax solution is typically colorless.

* Density: The density of a borax solution will vary depending on the concentration.

* Boiling Point: The boiling point of a borax solution will be higher than the boiling point of pure water.

* Freezing Point: The freezing point of a borax solution will be lower than the freezing point of pure water.

Let me know if you'd like to explore any of these properties in more detail!