Question:
The oxidation states of transition metal atoms in $\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}$, $\mathrm{KMnO}_{4}$ and $\mathrm{K}_{2} \mathrm{FeO}_{4}$, respectively, are $x, y$ and $z$. The sum of $x, y$ and $z$ is_____________
Solution:
(19)
