According to the definition of transition metals the elements should have incomplete penultimate $(n-1)$ shell.
But few $d$-block elements have completely filled penultimate shell, they are not considered as transition metals.
e.g., ${Zn}\left(3 d^{10} 4 s^2\right), \quad {Cd}\left(4 d^{10} 5 s^2\right)$ and $\operatorname{Hg}\left(5 d^{10} 6 s^2\right)$
