NH3    +    H2O    -->    OH-    +    NH4+

This is a chemical reaction showing the formation of hydroxide ions (OH-) and ammonium ions (NH4+) from ammonia (NH3) and water (H2O). Here's the step-by-step process:

1. Ammonia (NH3) and water (H2O) are the reactants in this reaction.

2. In the reaction, a hydrogen ion (H+) from water is transferred to ammonia.

3. The transfer of the hydrogen ion results in the formation of ammonium (NH4+).

4. The remaining part of the water molecule becomes a hydroxide ion (OH-).

5. The products of the reaction are therefore hydroxide ions and ammonium ions.

This reaction is an example of a Bronsted-Lowry acid-base reaction, where water acts as an acid (donating a proton) and ammonia acts as a base (accepting a proton).