The formula of lithium nitride is Li3N, where N contains (−)3 charge. Thus, formula of nitride-ion =N3− ∵ For a neutral atom, atomic number = number of protons and number of protons = number of electrons Also, atomic number of nitrogen (N)=7 ∴ It has 7 protons and due to (−)3 charge, it has 7+3=10 electrons. ∴ Hence, (c) is the correct answer.