The oxidation state of $\mathrm{Mn}$ in $\mathrm{KMn}{0}_4$ is

K+ and ${\mathrm{MnO}}_4$ separate from $\mathrm{KMn}{0}_4$ . Consequently, we shall now determine the $\mathrm{Mn}$ oxidation number.
Assume it is in the oxidation state X. Consequently, the formula is +1+ X 8 = 0.
Therefore, X has a value of +7.

Since $\mathrm{KMn}{0}_4$ has an overall oxidation number of 0, the equation has been expressed in that way. K has an oxidation number of one, while O has a value of two. The oxidation number of four oxygen atoms will therefore be 8.
Since the oxidation numbers on both sides should be equal, we have a value of +7.