Question

\[{{S}}{{{O}}_{{2}}}\] reduces \[{{MnO}}_{{4}}^{{ - }}\] to \[{{M}}{{{n}}^{{{2 + }}}}\]. Number of electrons involved in the reduction of \[{{MnO}}_{{4}}^{{ - }}\] to \[{{M}}{{{n}}^{{{2 + }}}}\] is:

Answer 1

Hint: Oxidation is the loss of electrons and reduction is the process of gain of electrons and the oxidation number of an atom is a number that gives information of the total number of electrons lost or gained by it. Most of the elements undergo oxidation to get stability.

Complete step by step answer:
There are certain rules for finding the oxidation number, they are,
A.Oxidation number of a free element is zero.
B.Oxidation number for monatomic ions is the net charge corresponding to the ion.
C.Oxidation number of a hydrogen atom is \[ + 1\]., but when it is bonded to an element with less electronegativity, the oxidation number is \[ - 1\,\].
D.Oxidation number of oxygen is \[ - 2\]in most of its compounds, but in peroxides, the oxidation is \[ - 1\,\].
E.Oxidation number of alkali metals are \[ + 1\] in their compounds.
F.Oxidation number of all alkaline earth metals (group 2 elements) are \[{{ + 2}}\] in their compounds.
G.Oxidation number for a halogen (group 17 elements) is \[ - 1\,\].
H.Oxidation number in the case of neutral compound is the sum of all the oxidation numbers of the constituent atoms
I.Oxidation number of a polyatomic ion is the sum of all the oxidation numbers of the atoms that constitute them equals the net charge of the polyatomic ion.
Here, let \[{{x}}\] be the oxidation no. of \[{{Mn}}\] in \[{{MnO}}_4^ - \]​, then
\[{{ - }}{{x + 4 \times ( - 2) = - 1}}\]
\[{{x = + 7}}\]
Thus the oxidation number of \[{{Mn}}\] in \[{{MnO}}_4^ - \] is \[{{ + 7}}\] and the oxidation number of \[{{Mn}}\] in \[{{M}}{{{n}}^{{{2 + }}}}\] is \[{{ + 2}}\].
Here the oxidation number of manganese changes from +7 to +2, therefore, number of electrons involved in the reduction of \[{{MnO}}_4^ - \]​ to \[{{M}}{{{n}}^{{{2 + }}}}\] is \[{{5}}\].
Hence the answer is \[{{5}}\]

Note: Some common redox reactions are, Combustion reaction, is a type of redox reaction which occurs between oxygen and compound to form oxygen containing products, Disproportionation reaction, It is a type of redox reaction in which a single reactant is reduced and oxidized. It is also known as an auto-oxidation reaction.