Which of the following are example of polyatomic and monatomic ions respectively?

Monoatomic ions are essentially substances that have either gained (positive) or lost (negative) electron/s.

For example, ${\mathit{Na}}^{\mathit{+}}$ represents a monatomic ion of sodium with a positive charge.

On the other hand, polyatomic ions have an electrical charge and two or more atoms that are covalently bound.

One common example is the ammonium ion, ${{\mathit{NH}}_4}^{\mathit{+}}$. The ammonium ion consists of a nitrogen atom bonded to four hydrogen atoms, and it carries a positive charge.