The decomposition of water into hydrogen gas h2 and oxygen gas o2 can be moldled by the balanced chemical equation

The equation is
H2O - > H2 + O2
Now, it should be balanced. In order to balance it, the amount of atoms on the both sides must be the same. There is one O atoms on the left side an two on the right. In order to balance the equation, write a coefficient 2 in front of H2O
2 H2O - > H2 + O2
But now there are four H atoms on the left and two on the right. Thus, you should write a 2 in front of the H2, too.
2 H2O - > 2 H2 + O2