: For stable molecule the value of bond order must be positive as bond order

no. of bonding electrons - no, of antibonding electrons

= .

2

The electrons in the bonding molecular orbital leads to lowering in energy and hence stability whereas in antibonding molecular orbital leads to destability.
(i) (-ve) bond order greater number of elcctrons in antibonding molectlat otbital than bonding molecular orbital. Therefore molecule is less stable compared to the separated atoms.

(ii) 0 bond order number of bonding molccular orbital number of antibonding molecular orbital. Therefore there is no gain in energy in forming the molecule.

(iii) ( bond order number of electrons in bonding molecular orbital is more than those in antibonding molecular orbital. Therefore there is a gain in energy while the bonding takes place.