Identify the oxidant and reduction in the following reactions.
(a) `Zn(s) +1/2 O_2(g)rarrZnO(s)`
(b) `CH_4(g) + 4Cl_2(g) rarr "CCl"_4(g) + 4HCl(g)`
(c) `I_2(aq) +2S_2O_3^(2-)(aq)rarr2I^(-) (aq)+S_4O_6^(2-)(aq)`
(d) `Zn(s)+2H^(+)(aq) rarr Zn^(2+) +(aq) +H_2(g)`

Explanation

(a) `Zn(s) +1/2O_2(g) rarr ZnO(s)`
In this reaction, zinc donates electrons to O to give zinc ions and oxide ions. Thus, Zn acts as reluctant while oxygen acts as oxidant.
(b) `CH_4(g)+4Cl_2(g)rarr"CCl"_4 (g) + 4HCl(g) CH_4` is oxidised and acts as reluctant while `Cl_2` is reduced and acts as oxidant.
(c) `I_2(aq)+2S_2O_3^(2-)(aq) rarr 2I^(-)(aq) +S_4O_6^(2-)(aq)`
`I_2` gains electrons and is reduced . Therefore , it acts as oxidant. `S_2O_3^(2-)` acts as reluctant.
(d) `Zn(s)+2H^(+)(aq) rarr Zn^(2+) (aq) +H_2(g)`
Zinc loses electrons and gets oxidised . Therefore , it acts as reluctant . Hydrogen gets reduced and acts as an oxidant.