Which of the following can be considered to be a transition element - Zn, Cd and Au ?

Explanation

`Zn(3d^(10)4s^(2)), Cd(4d^(10)5s^(2))` and `Au(5d^(10)6s^(1))`.
Of these three elements, Au is considered to be a transition element. The highest oxidation state of Au is + 3, and in this state, its electronic configuration is `5d^(8)`. Since `Au^(3+)` has incompletely filled d - orbital, Au is considered as a transition element. On the other hand, the highest oxidation state of Zn and Cd are + 2 and in this state, the electronic configurations of Zn and Cd are `3d^(10)` and `4d^(10)`, respectively. As they have completely filled d - orbitals both in the elemental state and also in the highest oxidation state, they are not considered as transition elements.