The correct option is C Zn
Metals that have incomplete d subshell either in neutral atom
or in their ions known as transition metals.
Zinc has the electronic configuration [Ar]3d104s2.and the configuration of the Zn2+ ion is [Ar]3d10. Thus, Zn is a non-transition metal.
Also, Cd, Hg of group 12 have full d10 configuration in their ground state as well as in their common oxidation states. Thus, both are non-transition metal.
Note: All transition elements are d-block elements, but all d-block elements are not transition elements.