When water boils, it's not oxygen and hydrogen that evaporate first. It's the water molecules themselves that change from liquid to gas.

Here's why:

* Water is a compound: Water (H₂O) is made up of two hydrogen atoms bonded to one oxygen atom. These atoms are tightly bound together.

* Boiling breaks bonds: Boiling provides enough energy to break the bonds between water molecules, allowing them to escape as water vapor (steam).

* Oxygen and hydrogen are released only in electrolysis: To separate oxygen and hydrogen from water, you need to use a process called electrolysis, which uses electricity to break the water molecule apart.

So, when you boil water, you're simply changing the state of the water from liquid to gas, not separating its individual elements.