The oxidation states of transition metal atoms in K 2 Cr 2 O 7 ,   KMnO 4 and K 2 FeO 4 , respectively,…

Compound  Oxidation state of transition element.

Oxidation states of K =+1 and O=-2

(i) ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7 \mathrm{x}=+6$
(ii) ${\mathrm{KMnO}}_4 \mathrm{y}=+7$
(iii) ${\mathrm{K}}_2{\mathrm{FeO}}_4 \mathrm{z}=+6$
so $(\mathrm{x}+\mathrm{y}+\mathrm{z})=19$