Which of the following molecular ions is diamagnetic?

Step-by-step solution

According to Molecular Orbital Theory (MOT), a species is diamagnetic if all its electrons are paired. (1) O ₂⁻ : 16 + 1 = 17 electrons. It has an odd number of electrons, hence it is paramagnetic. (2) N ₂⁺ : 14 - 1 = 13 electrons. It has an odd number of electrons, hence it is paramagnetic. (3) O ₂²⁻ : 16 + 2 = 18 electrons. Its molecular orbital configuration is: 1s^2, ^ * 1s^2, 2s^2, ^ * 2s^2, 2p_z^2, 2p_x^2 = 2p_y^2, ^ * 2p_x^2 = ^ * 2p_y^2 . Since all electrons are paired, it is diamagnetic. (4) C ₂⁺ : 12 - 1