🤓 Based on our data, we think this question is relevant for Professor Fortney's class at PITT.
We are asked to choose from the given reactions where the oxidation state of hydrogen changed.
We must identify the oxidation state of Hydrogen for each reaction, both in the reactant side and the product side. Let us look at each of the reactions and focus on compounds containing Hydrogen.
In which reaction does the oxidation number of hydrogen change?
1) CaO(s) + H2O(l) → Ca(OH)2(s)
2) 2Na(s) + 2H2O(l) → 2NaOh(aq) + H2(g)
3) SO2(g) + H2O(l) → H2SO3(aq)
4) HCl(aq) + NaOH(aq) → NaCl(aq) + H 2O(l)
5) HClO4(aq) + CaCO3(s) → Ca(ClO4)2(aq) + H2O(l) + CO2(g)