Answer:
B. 22 units.
Explanation:
A perpendicular dropped from center to a chord bisects the chord.
In the given figure O is the center of the circle .OB is a perpendicular dropped from center of circle to the chord AC and hence it bisects the chord .
AB=BC= 11 units .
By addition of line segments :
Length of chord AC = AB+BC =11+11 = 22 units.