In the given figure we have a circle with center J.
By definition, the radius is the distance from its center to a point located on the circle.
a) In the given figure, a radius is JI
A diameter is a chord that passes through the center of the circle and it is twice the radius.
b) A diameter is KL.
A chord is a segment that connects two points on a circle.
c) A chord is HM.
d) If the length of JI (remember this is a radius) is 2 units, then the length of KL is twice this value: 2*2units= 4 units.