What is the diameter if the radius of a circle is 6?

To determine the diameter of a circle when the radius is given, you use the relationship between the diameter and the radius. The diameter of a circle is twice the length of the radius. This can be expressed with the formula:

Diameter = 2 × Radius.

In this case, if the radius is 6, you would calculate the diameter as follows:

Diameter = 2 × 6 = 12.

This confirms that the correct answer is 12, as it accurately reflects the mathematical relationship between a circle's radius and its diameter. Understanding this relationship is fundamental in geometry, especially when working with properties of circles.