* Binary compounds are composed of only two elements.

* Hydrogen sulfide (H₂S) consists of hydrogen (H) and sulfur (S).

* Sulfate (SO₄²⁻) is a polyatomic ion containing sulfur and oxygen.

* Ammonium (NH₄⁺) is a polyatomic ion containing nitrogen and hydrogen.

Since sulfate and ammonium contain more than two elements, they are not binary compounds.