<u>Manganese (VII) ion (an anion) has the formula MnO₄⁻</u>. A polyatomic ion is an ion that is made up of more than one atom. For example, MnO₄⁻ and NH₄⁺. Since the ion provided in the question is an anion, the polyatomic ion that would react with it will have to be a cation (positively charged).
<u>The polyatomic cation that will react with MnO₄⁻ to form a neutral compound is NH₄⁺ (ammonium ion) to form NH₄MnO₄ (Ammonium permanganate).</u>
