Chemistry - Complete d-block Question with Solution | TestHub

Transition elements are defined as elements which have incompletely filled d-orbitals in their ground state or in any of their common oxidation states.

Mercury (Hg) has the ground state electronic configuration $[Xe]4f^{14}5d^{10}6s^2$. In its common oxidation states (+1 and +2), the d-orbitals remain completely filled ($5d^{10}$).

Therefore, Hg is not regarded as a transition element, whereas Ni, Fe, and Ag have incompletely filled d-orbitals in their ground state or common oxidation states.

Answer: Hg