Question: what is the difference between covalency and oxidation state?
Answer: Covalency is the number of electrons shared by an atom with the other atoms to form covalent bonds, e.g., Carbon can share 4 electrons, so it has 4 covalency. Oxidation state is the number of electrons lose by an atom, e.g., Na+, Na loses one electron hence get a + charge, oxidation state is +1.