On what basis scandium is a considered as transition metal, but Zinc is not considered as transition metal?

on the basis of an incompletely filled 3d orbital in the case of Scandium atom in its ground state, but Zinc has completely filled 3d orbital in its ground and its oxidation state.

The correct answer is Option (2) → on the basis of an incompletely filled 3d orbital in the case of Scandium atom in its ground state, but Zinc has completely filled 3d orbital in its ground and its oxidation state.

A transition metal is defined as an element that has an incompletely filled d-subshell either in its atom or in one of its common oxidation states.

• Scandium (Sc):
  Electronic configuration = $[Ar]\,3d^1 4s^2$
  → It has an incompletely filled 3d orbital in its ground state.
• Zinc (Zn):
  Electronic configuration = $[Ar]\,3d^{10} 4s^2$
  → It has a completely filled 3d orbital in both its ground state and its common oxidation state ($Zn^{2+}: 3d^{10}$).

Therefore, Scandium is considered a transition metal, but Zinc is not.