Molecular Orbital Theory

Step 1: Bond Order Formula.
The bond order in a molecule is given by the formula:

Step 2: Bond Orders for Each Species.
- (A) He : For He , there are 2 electrons in bonding orbitals and 1 electron in antibonding orbitals. So, the bond order is: - (B) O : O has 10 bonding electrons and 7 antibonding electrons, so the bond order is: - (C) HF: HF is a simple molecule with a single bond between hydrogen and fluorine. The bond order is 1. - (D) NO : NO has 11 bonding electrons and 6 antibonding electrons, so the bond order is:

Step 3: Conclusion.
The increasing order of bond order is: So, the correct order is (A), (B), (C), (D), corresponding to option (1).