Here's why:

* Boiling Point: Boiling water simply means the liquid water is reaching its boiling point (100°C or 212°F). At this point, the water molecules gain enough energy to break free from the liquid state and transition into a gaseous state, which is called steam.

* Chemical Formula: Water in its gaseous form (steam) still retains the same chemical formula, H2O. It's the same molecule, just in a different physical state.

* Decomposition: For water to decompose into hydrogen gas (H2) and oxygen gas (O2), you need to supply a significant amount of energy through electrolysis. This process is not what happens when water boils.

So, while water changes from liquid to gas when it boils, it doesn't change its chemical composition. It's still H2O, just in the form of steam.