* Polyatomic ions are groups of two or more atoms that are covalently bonded together and carry a net electrical charge.

Here are some examples of polyatomic ions:

* Nitrate (NO₃⁻): This ion consists of one nitrogen atom and three oxygen atoms with a negative charge.

* Sulfate (SO₄²⁻): This ion consists of one sulfur atom and four oxygen atoms with a negative charge.

* Ammonium (NH₄⁺): This ion consists of one nitrogen atom and four hydrogen atoms with a positive charge.

Let's look at the other options:

* Neutral ions: These ions have no net charge. Atoms that are not ions are neutral.

* Positive ions: These ions have a positive charge (called cations). They can be made of single atoms (like Na⁺) or polyatomic groups (like NH₄⁺).

* Negative ions: These ions have a negative charge (called anions). They can also be made of single atoms (like Cl⁻) or polyatomic groups (like NO₃⁻).

Key takeaway: The defining characteristic of a polyatomic ion is that it's a group of multiple atoms covalently bonded together and carrying a charge.