Final answer:
The polyatomic ion in the compound KMnO₄ is permanganate (MnO₄) with a charge of -1.
Step-by-step explanation:
The compound KMnO₄ is called potassium permanganate. The polyatomic ion present in this compound is MnO₄, which is known as the permanganate ion. This ion has a charge of -1. Therefore, in the compound KMnO₄, the polyatomic ion permanganate (MnO₄) has a charge of -1.