In order to identify these mentioned terms, it is important that each of them is defined.
Diameter: It is a line that passes through the center of the circle from one endpoint to another. It is two times the radius of the circle
Radius: It is a line drawn from the center of the circle to one endpoint of the circle.
It is half of the diameter.
Chord: It is a line drawn from one endpoint of the circle to another but does not necessarily pass through the center. Diameter is an example of a chord, but a chord does not have to be a diameter
Arc: It is a segment of the circumference of a circle
Circumference: is the total distance around the circle
From the diagram above:
|AB| is a diameter
|OA| or |OB| is the radius
|CD| is the chord
Arc CD is indicated on the diagram
If a circle has a radius of 2 cm:
Diameter = 2 x radius
Diameter = 2 x 2
Diameter = 4 cm
Therefore, if a circle has a radius of 2 cm, the diameter is 4 cm