What is the oxidation number of manganese in potassium permanganate, $\mathrm{KMnO}_4$? (K is $+1$, O is $-2$ in non-peroxides.)

1. $\mathrm{KMnO}_4$ is a neutral molecule, so the sum of all oxidation numbers must be $0$. 2. Let Mn have oxidation number $x$. 3. Contributions: K = $+1$; O = $4 \times (-2) = -8$; Mn = $x$. 4. Sum to zero: $(+1) + x + (-8) = 0 \Rightarrow x = +7$. 5. This is the maximum possible oxidation state for Mn (its group number in the older nomenclature is 7). $+2$ is found in $\mathrm{MnCl}_2$, $+4$ in $\mathrm{MnO}_2$, and $+6$ in $\mathrm{K}_2\mathrm{MnO}_4$ (potassium manganate, a different compound). _Source: syllabus Chemistry Part 2, Ch 7, §7.3 (Oxidation Number, worked examples), pp. 4-6._