In which reaction does the oxidation number of hydrogen change? A) CaO (s) + H₂O (l) -Ca(OH)₂(s) B) HCl (aq) + NaOH (aq) -NaCl (aq) + H₂O (l) C) 2 Na (s) + 2 H₂O (l) -2 NaOH (aq) + H₂(g) D) 2 HClO₄(aq) + CaCO₃(s) -Ca(ClO₄)₂(aq) + H₂O (l) + CO₂(g) E) SO₂(g) + H₂O (l) -H₂SO₃(aq)

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In reaction C, hydrogen in water (H2O) has an oxidation number of +1, and in the product hydrogen gas (H2), it has an oxidation number of 0. This indicates a change in the oxidation number of hydrogen.

In Which Reaction Does the Oxidation Number of Hydrogen Change