Answer:
If the radius is perpendicular to a chord, the length of the chord is 13 units (option A).
Explanation:
AB=6.5 units
When a radius is perpendicular to a chord divides it into to equal parts, then:
AB=BC=6.5 units
Chord: AC=AB+BC
Chord: AC=6.5 units+6.5 units
Chord: AC=13 units