Question

The oxidation state of Mn in \[{{\text{K}}_2}{\text{Mn}}{{\text{O}}_4}\] is:
A. +5
B. +4
C. +7
D. +6

Answer 1

Hint: A number assigned to an element in a chemical combination which represents the number of electrons lost or gained by an atom is called its oxidation state.

Complete step by step answer:
Certain rules have been made, to follow while determining the oxidation state of an element in a compound. These rules are –
1) Alkali metal ions always have oxidation state of +1.
2) Alkaline earth metals have oxidation state of +2.
3) All hydrogens in protons \[{\text{(}}{{\text{H}}^ + }{\text{)}}\] have oxidation state +1 and in hydride it is -1.
4) Oxidation number of oxygen in oxide ion (${O_2}^-$) is -2.
So, the oxidation state of K will be +1, and that of $O_4$ will be \[{\text{4 }} \times {\text{ ( - 2) = - 8}}\].
Let the oxidation state of Mn be ‘x’.
Since there is no total charge on the molecule, the sum of all oxidation states will be 0.
Therefore -
\[
  {\text{2}} \times {\text{( + 1) + x + }}\left( { - 8} \right) = 0 \\
  {\text{2 + x - 8 = 0}} \\
  {\text{x - 6 = 0}} \\
  {\text{x = + 6}} \\
\]
So, the oxidation state of Mn in \[{{\text{K}}_2}{\text{Mn}}{{\text{O}}_4}\] is +6.
So, option D is correct.

Additional information:
An atom can have multiple valence electrons and can form multiple bonds. We assign the atom's oxidation state, assuming that these bonds are ionic. So, generally the oxidation state is equal to the number of electrons involved in bonding. Hence, oxidation state is a hypothetical case of assumption.

Note: If the given compound has no total charge, the sum of oxidation states of all the constituent atoms will be equal to zero. On the other hand, if a charged species is present, the sum of oxidation states of constituent atoms will be equal to the total charge present on the species whether positive or negative.