How to know the atomic number when two reactants react e.g.
H2+O2= H2O how it should give H2O2 or HO4
Atomic number is the number of protons in an atom. It is always remain fix and never change with reactions.
For example H stands for hydrogen. The atomic number of hydrogen is one (1). It will be always one doesn’t matter hydrogen reacts with which other atom.
We can check the atomic numbers of each atom in the periodic table as given below.
In the given reaction; H2, O2, H2O and H2O2 are molecules not atom. Molecules are formed by combination of atoms. Here also the atomic number of H is 1, O is 8 only.