Identify the oxidant and reductant in the following reactions:
a. `10H^(o+)(aq)+4Zn(s)+NO_(3)^(ө)(aq)rarr4Zn^(2+)(aq)+NH_(4)^(o+)(aq)+3H_(2)O(l)`
b. `I_(2)(g)+H_(2)S(g)rarr2HI(g)+S(s)`

Explanation

(a)
We observe that oxidation number of S increases from -2 (`"in"H_2S`) to 0 (in S) which means that `H_2S` is being oxidised or `H_2S` is acting as reluctant. The oxidation number of nitrogen decreases from +5 (in `NHO_3` ) to 2 in (NO) indicating that `HNO_3` is being reduced or `HNO_3` is acting as an oxidant.
(b)
We obseve that oxidation number of zinc increases from 0 (in Zn) to +2 (in `ZnSO_4` ) which means that Zn is being oxidised or zinc is acting as reductant . On the order hand, the oxidation number of copper decreases from +2 (in `CuSO_4` ) to 0 (in Cu), indicating that copper is being reduced or `CuSO_4` is acting as an oxidant.
(c)
Oxidation number of iodine decreases from 0 to -1 . Therefore , it is reduced and acts as an oxidant . The oxidation number of S in hydrogen sulphide increases from -2 to 0. Therefore , it oxidised and hence acts as reluctant.
(d)
Oxidation number of zinc increases from 0 to +2. Therefore , it is oxidised and acts as a reluctant. The oxidation number of N decreases from +5 to -3 and , therefore , it is reduced and acts an oxidant.