In which reaction does the oxidation number of hydrogen change?
O 2HCIO4 (aq) + CaCO3 (s)
Ca(CIO4)2 (aq) + Hâ‚‚O (1) + CO2(g)
O CaO (s) + Hâ‚‚O (1)
Ca(OH)2 (s)
O HCl(aq) + NaOH (aq)
NaCl (aq) + Hâ‚‚O (1)
O SO2 (g) + Hâ‚‚O (1)
Hâ‚‚SO3 (aq)
O 2Na (s) + 2Hâ‚‚O (1)
2NaOH (aq) + H2 (g)
