Rehoboam told Israel that where his father had scourged them with whips, he would use what?

Answer: Scorpions

Following his young advisers, Rehoboam said, "My father scourged you with whips; I will scourge you with scorpions." Israel then rebelled.

“and spoke to them as the young men had advised, saying, “Whereas my father made your yoke heavy, I will add to your yoke. Whereas my father scourged you with whips, I will scourge you with scorpions.””— 1 Kings 12:14 (BSB)