* Oxygen gas (O2): You have four oxygen atoms, which means you have two molecules of oxygen gas (O2).

* Hydrogen (H): You have two hydrogen atoms.

* Water (H2O): Each water molecule requires two hydrogen atoms and one oxygen atom.

The Reaction:

2 O2 + 2 H2 → 2 H2O

Explanation:

* The reaction uses up all the hydrogen atoms (2) to form two water molecules.

* It also uses up one oxygen molecule (O2) to form those two water molecules.

* You have one oxygen molecule (O2) leftover.

Answer: You can produce two molecules of water.