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 gound 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 sate as well as in its oxidised state, hence it is not regarded as a transition element.