Answer: 2 H₂ + O₂ → 2 H₂O
Reasoning:
When balancing an equation, what you are trying to do is to ensure that the amount of each atom on the right side (reactant side), is equal to the amount of each atom on the left side (product side), because of the law of conservation of energy.
∴ the balanced equation is 2 H₂ + O₂ → 2 H₂O