Here's a breakdown:

* NH4: This represents the ammonium ion (NH₄⁺). It's a positively charged ion made of one nitrogen atom and four hydrogen atoms.

* SO4: This represents the sulfate ion (SO₄²⁻). It's a negatively charged ion made of one sulfur atom and four oxygen atoms.

* (NH4)2: The subscript '2' indicates there are two ammonium ions in the compound.

Therefore, ammonium sulfate is a salt composed of two ammonium ions (NH₄⁺) and one sulfate ion (SO₄²⁻).

Key properties and uses of ammonium sulfate:

* Appearance: White crystalline solid

* Solubility: Soluble in water

* Uses:

* A major nitrogen-containing fertilizer

* Used in fire extinguishers

* Used in the production of textiles and paper

* Used as a food additive

Let me know if you have any other questions.