C

Step 1: Understand the definitions of the options provided:
- **Density** is a scalar quantity that describes mass per unit volume.
- **Magnetic flux** is also a scalar quantity, representing the total magnetic field passing through a given area.
- **Intensity of magnetic field** (often referred to as **magnetic field strength** or **magnetic field vector**) is a vector quantity, defined as the force experienced by a unit magnetic pole placed in a magnetic field. It has both magnitude and direction.
- **Magnetic potential** (or scalar magnetic potential) is a scalar quantity.

Step 2: Determine the vector nature:
Since **Intensity of magnetic field** has both magnitude and direction, it is classified as a vector quantity.
Therefore, the correct answer is C.