W
hen covalent bonds are broken and reformed, this may be a simple atom of an element changing to an ion or vice versa, a polyatomic ion rearranging to another ion or molecule, or a molecule rearranging to another molecule or an ion.

Oxalic Acid changes to Carbon Dioxide Net Ionic Change

O

xidation has taken place!
Covalent Bonds are broken and reformed with two electrons lost by the Oxalic Acid molecule when making the two Carbon Dioxide molecules and two hydrogen ions as products.