4) is a molecular ion. A molecular ion is a charged molecule that retains its chemical identity as a whole. it results from the loss or gain of one or more electrons by a molecule, resulting in a net electric charge. In the case of ammonium ion, four hydrogen atoms form covalent bonds with a central nitrogen atom, resulting in a positively charged ion with a molecular formula of NH+

4. The covalent bonds between the nitrogen atom and hydrogen provide a stable structure, preserving the molecular identity even in its ionic form.