Find the oxidation number of Mn, Cr and Cl in `KMnO_4, K_2Cr_2O_7` and `KClO_4` respectively.

Explanation

`{:("Mn in " KMnO_4,(+1) + x + (-8),"or" x = +7),("Cr in " K_2Cr_2O_7,(+2)+ 2x + (-14),"or" x = +6),("Cl in " KClO_4, (+1) + x + (-8),"or" x = +7):}`