If the diameter of a circle is 12 cm, what is the radius?

The radius of a circle is defined as half of its diameter. In this scenario, the given diameter of the circle is 12 cm. To find the radius, you simply divide the diameter by 2.

Calculating this gives:

[ \text{Radius} = \frac{\text{Diameter}}{2} = \frac{12 , \text{cm}}{2} = 6 , \text{cm}. ]

Thus, the radius is 6 cm, making the correct answer B. This understanding of the relationship between the diameter and radius of a circle is fundamental in geometry, as it allows one to easily determine one measurement when provided with the other.