Statement (A): Oxidation number of Mn in ${\text{KMnO}}_4$ is +7.

Statement (B): The oxidation number of an atom in its elementary form is zero.

Statement (C): Sodium exhibits +2 oxidation state.

(i) According to oxidation number rules, first two statements are correct, statement III is incorrect.

Oxidation state of Mn in ${\text{KMnO}}_4$

$\begin{array}{l}\Rightarrow +1+x+(-2\times 4)=0\\ +1+x+(-8)=0\\ x=+7\end{array}$

Sodium exhibits +1 oxidation state but not +2.

(ii) The oxidation number of an atom in its elementary form is zero.

(iii) Sodium exhibits +1   oxidation state because it is in IA group.