Balance the chemical equation: H2 + O2 -> H2O. What are the correct coefficients?

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

Answer: (C)

Balancing chemical equations means making sure the same number of each type of atom appears on both sides of the arrow, and you can only adjust coefficients, not the formulas themselves. For hydrogen gas reacting with oxygen gas to form water, look at how many hydrogens each molecule contributes and how many water molecules you plan to make. Each water molecule has two hydrogens, so to have four hydrogens on the product side you’d form two water molecules, which requires two H2 molecules on the reactant side. Now check oxygen: two H2O molecules contain two oxygens in total, which matches the one O2 molecule on the left (O2 has two oxygens). This balances both elements. Therefore the balanced equation is 2 H2 + O2 -> 2 H2O. The other layouts fail because they either don’t balance hydrogens, or don’t balance oxygens correctly, or both.