Balance the equation: H2 + O2 -> H2O. Which is the correct balanced form?

• A. 2 H2 + O2 -> 2 H2O
• B. H2 + O2 -> H2O
• C. 2 H2O -> 2 H2 + O2
• D. H2 + 2 O2 -> 2 H2O2

Answer: (A)

Balancing atoms on both sides ensures the law of conservation of matter. Each water molecule has 2 hydrogens and 1 oxygen, so to form water from H2 and O2 you need four hydrogens on the left. That requires two H2 molecules, and one O2 molecule provides the two oxygens needed for two H2O molecules. The result is 2 H2 + O2 -> 2 H2O, which matches hydrogen and oxygen counts on both sides. Other forms either depict the reverse reaction, or don’t conserve hydrogen or oxygen for the given direction, or would require different products.