Explanation:

Correct option 1: 5

Given

Six bells commence tolling together at 7:59 am
Toll intervals of 3, 6, 9, 12, and 15 seconds respectively.
Concept used:
Least Common Multiple (LCM)
Calculation:
A least common multiple of (3, 6, 9, 12, and 15) = 2 x 2 x 3 x 3 x 5 = 180 sec
Bells ring together after every 180 sec
Required number of times in 17 minutes (17 x 60 seconds)
⇒Number of times they toll together =(17×60) / 180
⇒ Number of times they toll together = 1020 / 180 = 5.7 ~ 5
This is approximated as 5 bells will not ring in fractions and, it will take some more time to bell 6th ring.
:. They toll together 5 times in 17 minutes.