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

Explanation

On the basis of incompletely filled 3d-orbitals in case of scandium atom in its ground state `(3d^(1))`, it is regarded as a transition element. On the other hand, zinc atom has completely filled d-orbitals `(3d^(10))` in its ground state as well as in its oxidised state, hence it is not regarded as a transition element.