Which of the following species has the longest bond length?

Step-by-step solution

According to Molecular Orbital Theory, the bond order of oxygen species can be calculated as: O ₂ (16 electrons): Bond order = 10 - 6 2 = 2 O ₂⁺ (15 electrons): Bond order = 10 - 5 2 = 2.5 O ₂⁻ (17 electrons): Bond order = 10 - 7 2 = 1.5 O ₂²⁻ (18 electrons): Bond order = 10 - 8 2 = 1 Bond length is inversely proportional to bond order. Since O ₂²⁻ has the lowest bond order (1), it will have the longest bond length. Answer: O ₂²⁻