Ammonium sulfate, (NH₄)₂SO₄, doesn't have a single oxidation number. Instead, each element within the compound has its own oxidation number. Here's how to break it down:

* Hydrogen (H): +1 (It's almost always +1 in its compounds)

* Nitrogen (N): -3 (To balance the four +1 from the hydrogens in ammonium, NH₄⁺)

* Sulfur (S): +6 (In sulfate, SO₄²⁻, the four oxygens each have a -2 charge, totaling -8. To balance this, sulfur has to be +6)

* Oxygen (O): -2 (Oxygen almost always has a -2 oxidation number in its compounds)

Important Note: The overall charge of the ammonium sulfate molecule is neutral (0). This is because the two ammonium ions (NH₄⁺) have a +1 charge each, while the sulfate ion (SO₄²⁻) has a -2 charge, making the total +2 - 2 = 0.