Ammonium hydroxide (NH₄OH) doesn't actually exist as a stable compound. It's a solution of ammonia (NH₃) in water. When this solution is heated or left exposed to air, the following happens:

1. Ammonia gas (NH₃) is released: The ammonia molecules escape from the solution as a gas. This is why ammonium hydroxide solutions have a strong, characteristic ammonia smell.

2. Water remains: The water that was part of the solution remains behind.

So, the "decomposition" of ammonium hydroxide is essentially the evaporation of ammonia from the solution, leaving behind water.

Here's the chemical equation:

NH₄OH (aq) → NH₃ (g) + H₂O (l)

Where:

* (aq) represents an aqueous solution

* (g) represents a gas

* (l) represents a liquid

It's important to note that the reaction is reversible. If ammonia gas is bubbled into water, it will dissolve and form a solution that behaves like ammonium hydroxide.