In the compound MnO4-, the oxidation number of manganese (Mn) can be determined by considering the known oxidation states of the other elements in the formula.
Oxygen (O) typically has an oxidation number of -2 in most compounds. Since there are four oxygen atoms in MnO4-, the total oxidation number contribution from oxygen is -2 * 4 = -8.
The overall charge of the compound is -1, as indicated by the minus sign in MnO4-. This means the sum of the oxidation numbers of all elements must add up to -1.
Let the oxidation number of manganese be x.
Now, we can set up the equation:
x + (-8) = -1
Solving for x:
x = -1 + 8
x = +7
So, in MnO4-, the oxidation number of manganese (Mn) is +7.