What is the oxidation number of manganese in `KMnO_(4)`? 

Explanation

A. `KMnO_(4)`
Let the oxidation number .Mn. = x
O.N.g .K. = +1
ON. Of oxygen = -2
`1 xx .K. + 1 xx .Mn. + 4 xx .0. = 0`
`1 xx (+1) + 1 xx (x) + 4 xx (-2) = 0`
`+1 + x - 8 =0`
`x- 7=0`
`therefore x = +7`
`therefore` ON.g Mn is `KMnO_(4) = + 7`
(b) `MnO_(4)^(-2)`
A. Let the O.N.g Mn = x
`1 xx Mn + 4 xx .0. = -2`
`1 xx (x) + 4 xx (-2) = -2`
`x - 8 = -2`
`x = +8 -2 = + 6`
`therefore` ON g Mn in `MnO_(8)^(-2) = + 6`