There are more hydrogen atoms on the right side of the arrow than on the left side.
From the equation, the total number of hydrogen atoms on the right-hand side is:
2 x 2 = 4.
On the left-hand side, the total number of hydrogen atoms is 2.
Considering the oxygen atom, there are 2 atoms on the right side as well as the left side of the equation.
Thus, the most correct way to construct the sentence is: There are more hydrogen atoms on the right side of the arrow than on the left side.