What is the oxidation number assigned to magnesium in KMnO4?

Oxygen is mostly negative besides linking with F (fluor).

Oxygen is mostly in - 2 oxidation states besides peroxide, superoxides.

Alkaline and alkaline-earth metals are respectively in + 1 and + 2 ox. states.

Normal molecule must be in 0 ox. state

K Mn O4 - oxidation state of Mn is "x". So,

(+1) + (x) + (2 * (-4)) = 0

x = 7