Calculate the oxidation number of each sulphur atom in the following compounds:

(a) Na₂S₂O₃ (b) Na₂S₄O₆

(ii) Will the reactivity of both the isotopes of hydrogen be the same towards oxygen? Justify your answer.

(Oxidation no. of every atom is underlined by red.)

(a) Na₂S₂O₃

(b) Na₂S₄O₆

(ii) The reactivity of isotopes of hydrogen is not same towards oxygen because of their different bond dissociation enthalpy. Deuterium and tritium have higher bond dissociation enthalpy than hydrogen thus their reactivity is also low.