Final answer:
Option (2), Victor reports the creature to the authorities after the murder of Elizabeth, which galvanizes him to take action against the creature he created.
Step-by-step explanation:
The event that finally makes Victor report the creature to the authorities is the murder of Elizabeth. This tragic event becomes a catalyst for Victor's actions, as it represents a profound personal loss and a direct attack on his loved ones by the creature he created. Victor's grief and sense of responsibility drive him to seek the help of the authorities to stop the creature and prevent further harm.