Question

Which of the following reactions is/are auto redox or induced oxidation reaction(s)?
(A)$Pb+{{O}_{2}}+{{H}_{2}}O\to PbO+{{H}_{2}}{{O}_{2}}$
(B) $N{{a}_{2}}S{{O}_{3}}+N{{a}_{3}}As{{O}_{3}}+{{O}_{2}}\to N{{a}_{2}}S{{O}_{4}}+N{{a}_{3}}As{{O}_{4}}$ ​
(C) $RCH=CHR+{{O}_{2}}+2{{H}_{2}}O\to 2RCH=O+2{{H}_{2}}{{O}_{2}}$ ​
(D) ${{P}_{4}}+{{(OH)}^{-}}\to P{{H}_{3}}+{{H}_{2}}P{{O}_{2}}^{-}$

Answer 1

Attempt this question by understanding about the auto redox reaction. Auto redox reaction is also known as induced oxidation reaction. In here, the same substance or a reactant oxidizes as well as reduces that is some part of it gets oxidized and some part of it gets reduced. So we will apply this definition to the given reactions in the question to obtain an answer.

Complete answer:
Let us first understand about the auto redox reaction:-
-Auto redox reaction (also known as induced oxidation reaction) is a reaction in which the same substance or the reactant oxidizes as well as reduces simultaneously, that is some part of it gets oxidized and some part of it gets reduced.
-To check which reaction is auto redox reaction, we will compare the oxidation states of all atoms of substances on both the side and check whether any reactant have been oxidized as well as reduced or not:-
(A)$Pb+{{O}_{2}}+{{H}_{2}}O\to PbO+{{H}_{2}}{{O}_{2}}$
For Pb:-

Reactant side	Product side
Pb = 0	Pb = +2

Pb only gets oxidized.
For ${{O}_{2}}$ :-

Reactant side	Product side
O = 0	O = -1 (in ${{H}_{2}}{{O}_{2}}$), -2 (in PbO)

${{O}_{2}}$ only gets reduced.
For ${{H}_{2}}O$ :-

Reactant side	Product side
O = -2	O = -1 (in ${{H}_{2}}{{O}_{2}}$)

${{H}_{2}}O$ only gets oxidized.
Since all reactants either get reduced or oxidized, so it is not an auto redox reaction.
(B) $N{{a}_{2}}S{{O}_{3}}+N{{a}_{3}}As{{O}_{3}}+{{O}_{2}}\to N{{a}_{2}}S{{O}_{4}}+N{{a}_{3}}As{{O}_{4}}$
For $N{{a}_{2}}S{{O}_{3}}$:-

Reactant side	Product side
S = +4	Pb = +6

$N{{a}_{2}}S{{O}_{3}}$ only gets oxidized.
For $N{{a}_{3}}As{{O}_{3}}$ :-

Reactant side	Product side
As = +3	As = +5

$N{{a}_{3}}As{{O}_{3}}$ only gets oxidized.
For ${{O}_{2}}$ :-

Reactant side	Product side
O = 0	O = -2 (in both $N{{a}_{2}}S{{O}_{3}}$ and $N{{a}_{3}}As{{O}_{3}}$)

${{O}_{2}}$ only gets reduced.
Since all reactants either get reduced or oxidized, so it is not an auto redox reaction.
(C) $RCH=CHR+{{O}_{2}}+2{{H}_{2}}O\to 2RCH=O+2{{H}_{2}}{{O}_{2}}$ ​
For ${{O}_{2}}$ :-

Reactant side	Product side
O = 0	O = -1 (in ${{H}_{2}}{{O}_{2}}$), -2 (in PbO)

${{O}_{2}}$ only gets reduced.
For ${{H}_{2}}O$ :-

Reactant side	Product side
O = -2	O = -1 (in ${{H}_{2}}{{O}_{2}}$)

${{H}_{2}}O$ only gets oxidized.
$RCH=CHR$ only got oxidized by addition of oxygen atom.
Since all reactants either get reduced or oxidized, so it is not an auto redox reaction.
(D) ${{P}_{4}}+{{(OH)}^{-}}\to P{{H}_{3}}+{{H}_{2}}P{{O}_{2}}^{-}$
For ${{P}_{4}}$ :-

Reactant side	Product side
P = 0	P = -3 (in $P{{H}_{3}}$), +1 (in ${{H}_{2}}P{{O}_{2}}^{-}$ )

${{P}_{4}}$ gets reduced as well as oxidized simultaneously. Therefore it is a case of auto redox reaction.
-Hence, the correct answer is: (D) ${{P}_{4}}+{{(OH)}^{-}}\to P{{H}_{3}}+{{H}_{2}}P{{O}_{2}}^{-}$

Note:
Even if one reactant or substance shows oxidation as well as reduction, then we may consider the reaction as an auto redox reaction without any further checking.
-Also in the following reactions:-
$Pb+{{O}_{2}}+{{H}_{2}}O\to PbO+{{H}_{2}}{{O}_{2}}$ and $RCH=CHR+{{O}_{2}}+2{{H}_{2}}O\to 2RCH=O+2{{H}_{2}}{{O}_{2}}$, if these were shown as reversible reactions then we may categorize it as auto redox reaction because ${{H}_{2}}{{O}_{2}}$ get reduced and oxidized to produce ${{H}_{2}}O$ and ${{O}_{2}}$ respectively.