Correct option is (B) 12 cm
We know that perpendicular from centre of the circle on any chord bisects the chord.
Since, OM \(\bot\) AB
\(\therefore\) OM bisect chord AB
\(\Rightarrow\) M is mid-point of chord AB
\(\Rightarrow\) AB = 2AM
\(=2\times6\) \((\because\) AM = 6 cm)
= 12 cm