In the reactions gives below, identify the species undergoing oxidation and reduction:
(i) H₂S(g) + Cl₂(g) → 2HCl(g) + S(s)
(ii) 3Fe₃O₄(s) + 8Al(s) → 9Fe(s) + 4Al₂O₃(s)
(iii) 2Na(s) + H₂(g) → 2NaH(s)