Bond Parameters

To determine the correct order of decreasing bond order among the given options, we need to calculate the bond order for each molecule or ion. Bond order can be derived using molecular orbital theory and is calculated as:
Bond Order =

Based on the calculations, the correct order of decreasing bond order is:

This is because , , and all have a bond order of 2, but typically this order reflects the impact of electron configurations and molecular stability, with being slightly more stabilized in its configuration, thus leading to this descending order.