Which of the following rules is not correct for assigning oxidation states (or numbers)?
a. Oxygen will normally have an oxidation state of -2.
b. When you have elements that don't fit into the scheme for the rules for determining oxidation states, you generally allow the more electronegative element to receive as many electrons as possible to achieve a noble gas configuration.
c. An oxidation number should add up to the charge on the most electronegative atom in the molecule.
d. Oxygen can have an oxidation state greater than -2 in cases where there is an elemental molecule (e.g., O2?) or when the oxygen atom is connected to a more electronegative element.