What is elements of third transition series?

                                           

• The third transition series starts from hafnium (Z=72) in which the filling of 5d subshell begins.
• The outer electronic configuration of hafnium is 4f14 5d2 6s2.
• This process continues thereafter in tantalum (Z=73), tungsten (Z=74), rhenium (Z=75), osmium (Z=76), iridium (Z=77), platinum (Z=78), gold (Z=79), and mercury (Z=80).
• The 5d subshell gets enlarged by the addition of one electron at each step and gets completed when mercury (Z=80) is reached, its outer electronic configuration being 5d10 6s2.
• since mercury and its common ions have their d orbitals completely filled, it should by definition, be excluded from the d block elements.