# Question #ee902

Feb 15, 2017

Mn O.N =+7

#### Explanation:

We all know oxygen has an oxidation number = 2
So when we have a charge on the molecule.
It means the sum of all the oxidation number of the molecule should add up to give that charge.
Like the ex. You have asked $M n {O}_{4}^{-}$
The molecule has -1 as the charge.
So,
(O.N of Mn + O.N of Oxygen should equal to -1)
We all know oxidation number(O.N) of O is -2
So,
Let X be the O.N of Men
$X + \left(- 2 \ast 4\right) = - 1$
I.e. $X - 8 = - 1$
Or X=-1+8
I.e. X=+7

Hope you understand. :)