How do you calculate the oxidation number of an ion?
For simple ions, i.e.
For more complex ions, the SUM of the oxidation numbers equals the charge on the ion. The sum of the oxidation numbers also equals the charge on the molecule in a NEUTRAL molecule.
Given what I have said the oxidation number of
I don't what level you are at. If you are at A level, you simply have to know what I wrote in the opening statement. If you are an undergrad you do have to know how to assign oxidation states in more complicated molecules and ions. Good luck.