The radius of a cylinder is half of its diameter. Given that the diameter is 16 units, the radius can be calculated as follows:
\[ \text{Radius} = \frac{\text{Diameter}}{2} = \frac{16 \text{ units}}{2} = 8 \text{ units} \]
Therefore, the radius of the cylinder is 8 units. The correct answer is:
- 8 units