Concept: The question tests on the basics of LCM.

Solution:
 

The bells toll together for the first time at at a time

=LCM(2,4,6,8,10,12)

= 120 sec = 2min

30 min has 15 such 2 min and hence the bells must have tolled together for 15 min and add 1 to it to represent their tolling together for the first time at t=0 sec.

Hence 16 times(Option D)