**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