What effect does oxidation have on the oxidation number of an element?

Oxidation involves the loss of electrons from an atom or ion, which results in an increase in its oxidation number. When an element undergoes oxidation, it typically transitions from a lower oxidation state to a higher one because the removal of electrons makes it more positively charged or less negatively charged. For instance, when you consider metals like iron or copper, upon oxidation, they lose electrons and transition from a neutral state to a cationic form, thereby raising their oxidation numbers. This principle applies broadly in redox reactions where an increase in oxidation number confirms that oxidation has taken place. Thus, the correct answer reflects the fundamental concept that oxidation corresponds directly to an increase in oxidation number.