Question

6. The oxidation number of Mn in KMnO4 is A) +8. B) +7. C) +5. D) -7. E) -8.

Answer 1

The oxidation number of Mn in $KMnO_4$  is +7.

Explanation:

In a compound  the sum of the oxidation states of all the atoms will be to equal the total charge on the ions.

$KMnO_4$ is neutral hence its total charge is zero

Oxidation number of  potassium+ Oxidation number of Manganese+Oxidation number of  Oxygen=0

We Know that

Oxidation number of  potassium= +1

Oxidation number of  Oxygen=  -2

 Substituting the values,

(+1)+ Oxidation number of  Manganese+ 4(-2)=0

(+1)+ Oxidation number of  Manganese+ (-8)=0

(-7)+ Oxidation number of  Manganese=0

Oxidation number of  Manganese= +7

Answer 2

Answer:

$kmno4 = 0\\ k(potassium) = + 1 \\ mn(manganese) = x\\ o(oxygen) = - 2 \\ \\ (+ 1) + x + ( - 2)4 = 0 \\ 1 + x - 8 = 0 \\ x = + 8 - 1 \\ x = + 7$