Question

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

Answer 1

If the orbitals of elements are completely filled in the ground as well as in their common oxidation state, it is not considered as transition element.

Zinc $(z=30)-3d^{10}4s^2\to$ outermost electronic configuration

$Z{n}^{+2}\to 3d^{10}4s^{\circ }\to$ In both cases Zn has completely filled d orbital.

Scandium $(Z=21)-3d^{1}4s^2\to$ outermost electronic configuration

$S{c}^{+3}\to 3d^{\circ }4s^{\circ }Sc\to$ in the ground state has incompletely filled d orbital