Question

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

Answer 1

$\text{Transition elements}$

Transition elements (also known as transition metals) are elements that have partially filled $d$ orbitals. IUPAC defines transition elements as an element having a $d$ subshell that is partially filled with electrons, or an element that has the ability to form stable cations with an incompletely filled $d$ orbital.

$\text{Why Zn is not a transition element?}$

On the basis of incompletely filled $3d$ orbitals in case of scandium atom in its ground state $\left(3d^1\right)$, it is regarded as a transition element.

On the other hand, zinc atom has completely filled d orbitals $\left(3d^{10}\right)$ in its ground state as well as in its oxidised state, hence it is not regarded as a transition element.