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

Explanation

According to definition, transition elements are those which have partially filled d-subshells in their elementary state or in their commonly occurring oxidation states. Scandium (Z = 21) has partially filled d-subshell (`3d^1`) and is therefore, a transition element. On the other hand, zinc (Z = 30) has the configuration`3d^(10)4s^2` . It does not have partially filled d-subshell in its elementary form or in commonly occurring oxidation state `(Zn^(2+) : 3d^10)` . Therefore, it is not regarded as transition element.