The formal charge of the nitrogen atom in the ammonium ion NH4+ can be calculated using the following formula:Formal charge = Valence electrons of the atom - Non-bonding electrons - 0.5 * Bonding electrons For nitrogen in NH4+, the number of valence electrons is 5 as nitrogen is in group 15 of the periodic table . In the ammonium ion, nitrogen forms 4 single bonds with 4 hydrogen atoms, so there are no non-bonding electrons and 8 bonding electrons 2 electrons per bond .Now, we can calculate the formal charge:Formal charge = 5 - 0 - 0.5 * 8Formal charge = 5 - 4Formal charge = +1So, the formal charge of the nitrogen atom in the ammonium ion NH4+ is +1.