Very pure hydrogen (99.9%) can be made by which of the following methods?

Pure hydrogen can be obtained from the electrolysis of water. Cathode (reduction): 2H₂O(l) + 2e⁻ → H₂(g) + 2OH⁻(aq) Anode (oxidation): 4OH⁻(aq) → O₂(g) + 2H₂O(l) + 4e⁻ Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen: Overall reaction: 2H₂O(l) → 2H₂(g) + O₂(g) The number of hydrogen molecules produced is thus twice the number of oxygen molecules.