The correct option is A 7
The oxidation number of oxygen is -2. The overall oxidation number of MnO−4 is -1. Let's consider the oxidation state of manganese to be 'x'. So, the equation will be:
x + 4× (-2) = −1
⟹x = −1 + 8
⟹x = 7
Therefore, the oxidation number for manganese is 7.