In the reactions given below , identify the species undergoing oxidation and reduction :
(i) `H_(2)S (g) + Cl_(2)(g) to 2 HCl (g) + S(s)`
`(ii) 3 Fe_(3)O_(4) (s) + 8 Al (s) to 9 Fe (s) + 4 Al_(2)O_(3)(s) `
(iii) `2 Na(s) + H_(2)(g) to 2 NaH (s)`