What was the bronze snake called that King Hezekiah broke into pieces?

Answer: Nehushtan

Israel had been burning incense to the bronze snake Moses had made, so Hezekiah destroyed it. It was called Nehushtan.

“He removed the high places, shattered the sacred pillars, and cut down the Asherah poles. He also demolished the bronze snake called Nehushtan that Moses had made, for up to that time the Israelites had burned incense to it.”— 2 Kings 18:4 (BSB)