The number of electrons that must be added to or removed from an atom in a combined state to convert it into its elemental form is equal to the oxidation state of the atom in the combined state.

Here's why:

* Oxidation state represents the charge an atom would have if all the electrons in its bonds were assigned to the more electronegative atom.

* Elemental form means the atom exists as a neutral species with no net charge.

Example:

* In NaCl (sodium chloride), sodium (Na) has an oxidation state of +1, while chlorine (Cl) has an oxidation state of -1.

* To convert sodium from its combined state in NaCl to its elemental form (Na), we need to add one electron to neutralize the +1 charge.

* To convert chlorine from its combined state in NaCl to its elemental form (Cl), we need to remove one electron to neutralize the -1 charge.

Key Point:

The number of electrons added or removed is directly related to the oxidation state. If the oxidation state is positive, electrons need to be added, and if it's negative, electrons need to be removed.