Atomic number of mercury = 80 and its electronic configuration is [Xe] 4f¹⁴, sd¹⁰, 6s². Mercury –mercury bonding is very weak because its valence electrons are not shared readily. In fact mercury is the only metal that does not form diatomic molecules in gas phase and its d-subshell is completely filled. Thus it prevents d-d overlapping.

Electrons exchange orbitals in order to stabilizes themselves. The energy released is called exchange energy and it depends on how many electrons are occupied in the orbitals plus their symmetrical distribution. Half filled and full filled subshells provide more stabilization (more exchange energy) due to their symmetrical nature.

Hence the six unpaired electrons present in f-shell can exchange 15 electrons.

Bromobenzene will not react with AgNO₃ in the presence of HCl, because in bromobenzene, already halogen is present and which is directly attached to benzene ring. Hence reaction is not possible.

Benzyl Chloride or α – chlorotoluene is an organic compound , which is a colorless liquid and is a more reactive organic compound. Hence it is widely used chemical building block.

The bonding of CO to a metal as consisting of two components. The first component is a two electron donation of the lone pair on carbon into a vacant metal d-orbiatl. This electron donation makes the metal more electron rich and in order to compensate for this increased electron density, a filled metal d-orbital may interact with the empty pi* orbital on the carbonyl ligand to relieve itself of the added electron density. This second component is called pi-back bonding. Or pi-back donation. The two components of this bonding are synergistic.

The more sigma donation by the carbonyl, stronger is the pi-back bonding interaction. The occupation of pi* on CO does leads to a decreased bond order in CO molecule itself. Hence bond order between Ni-C bond is more than two.