Answer:
2
Step-by-step explanation:
H2O2 ➞ 2 H2O + O2
The reaction is currently not balanced because the number of atoms on the reactant side is not equal to that of the product side
Hydrogen
Reactant = 2 Product = 4
Oxygen
Reactant = 2 Product = 4
Adding 2 to H2O2 balances the reaction as the number of atoms of both elements are now balanced on both sides of the equation
2H2O2 ➞ 2 H2O + O2