Why Cadmium and Zinc are considered as Transition metals

Zinc, cadmium, and mercury are not transition metals.[2] as they have the electronic configuration [ ]d10s2, with no incomplete d shell.[5] In the oxidation state +2 the ions have the electronic configuration [ ] d10. While these elements can exist in the +1 oxidation state, as in the diatomic ion Hg22+, there are no unpaired electrons because of the formation of a covalent bond between the two atoms of the dimer. The group 12 elements Zn, Cd and Hg may be classed as post-transition metals.