1. Determine the chemical formula of ammonium sulfide:

* Ammonium is NH₄⁺

* Sulfide is S²⁻

* To balance the charges, we need two ammonium ions for every sulfide ion: (NH₄)₂S

2. Calculate the number of hydrogen atoms per molecule:

* Each ammonium ion (NH₄⁺) has 4 hydrogen atoms.

* The formula (NH₄)₂S indicates there are 2 ammonium ions per molecule.

* Therefore, there are 4 hydrogen atoms/ion * 2 ions/molecule = 8 hydrogen atoms per molecule of ammonium sulfide.

3. Calculate the total number of hydrogen atoms:

* We have 4.00 mol of ammonium sulfide.

* Avogadro's number tells us there are 6.022 x 10²³ molecules in 1 mole.

* Therefore, we have 4.00 mol * 6.022 x 10²³ molecules/mol = 2.409 x 10²⁴ molecules of ammonium sulfide.

* Finally, multiply the number of molecules by the number of hydrogen atoms per molecule: 2.409 x 10²⁴ molecules * 8 hydrogen atoms/molecule = 1.93 x 10²⁵ hydrogen atoms

Therefore, there are approximately 1.93 x 10²⁵ hydrogen atoms in 4.00 mol of ammonium sulfide.