In the reactions given below, identify the species undergoing oxidation and reduction:
(i) CH4(g) + 2O2(g) ⟶ CO2(g) + 2H2O(l)
(ii) 2H2S(g) + O2(g) ⟶ 2S(s) + 2H2O(l)
(iii) CH2 = CH2(g) + H2(g) ⟶ H3C — CH3(g)
(iv) 2HgO(s) ⟶(Δ) 2Hg(l) + O2(g)
(v) Mg(s) + S(s) ⟶ MgS(s)
(i) CH4 is oxidized to CO2 while O2 is reduced to H2O.
(ii) H2S is oxidized to S while O2 is reduced to H2O.
(iii) CH2 = CH2 is reduced to CH3—CH3 while H2 is oxidized to CH3—CH3.
(iv) Hg2+ is reduced to Hg while O2− is oxidized to O2.
(v) Mg is oxidized to Mg2+ while S is reduced to S2−.