Here's why:

* Scalar: A scalar quantity has only magnitude (size or amount). Examples include temperature, mass, and speed.

* Vector: A vector quantity has both magnitude and direction. Examples include velocity, force, and displacement.

Viscosity describes the resistance of a fluid to flow. It tells us how "thick" or "sticky" the fluid is. It doesn't have a direction associated with it. For example, honey has a higher viscosity than water, but there's no directional component to that statement.