Step 1: Bond Order Calculation Formula.
The bond order of a molecule is determined by the following formula:\[\text{Bond Order} = \frac{\text{Number of bonding electrons} - \text{Number of antibonding electrons}}{2}\]
Step 2: Bond Order Determination for Each Species.
- (A) He\(_2^+\): This species has 2 bonding electrons and 1 antibonding electron, resulting in a bond order of:\[\text{Bond Order} = \frac{2 - 1}{2} = 0.5\]- (B) O\(_2^-\): With 10 bonding electrons and 7 antibonding electrons, the bond order is:\[\text{Bond Order} = \frac{10 - 7}{2} = 1.5\]- (C) HF: HF is a diatomic molecule with a single bond, giving it a bond order of 1.- (D) NO\(^-\): This ion possesses 11 bonding electrons and 6 antibonding electrons, leading to a bond order of:\[\text{Bond Order} = \frac{11 - 6}{2} = 2.5\]
Step 3: Final Ordering.
The species arranged in increasing order of bond order are:\[\text{He}_2^+ (0.5) < \text{O}_2^- (1.5) < \text{HF} (1) < \text{NO}^- (2.5)\]Therefore, the correct sequence is (A), (B), (C), (D), corresponding to option (1).