* Ammonia (NH₃): Each ammonia molecule has 1 nitrogen atom and 3 hydrogen atoms, for a total of 4 atoms.

* Nitrogen (N₂): A nitrogen molecule has 2 nitrogen atoms.

* Hydrogen (H₂): A hydrogen molecule has 2 hydrogen atoms.

The Reaction:

2 NH₃ → N₂ + 3 H₂

Counting the Atoms:

* Reactants: 2 ammonia molecules have 2 x 4 = 8 atoms.

* Products:

* 1 nitrogen molecule has 2 atoms.

* 3 hydrogen molecules have 3 x 2 = 6 atoms.

* Total product atoms: 2 + 6 = 8 atoms.

Conclusion:

There will be a total of 8 atoms present after the reaction, the same number as in the reactants. This demonstrates the law of conservation of mass, where the total number of atoms remains constant in a chemical reaction.