Scandium (Z=21) does not exhibit variable oxidation states.
All the d-blocks elements exhibit various valencies or have variable oxidation number. But scandium does not show because scandium has partially filled d-orbitals in the ground state. In the case of scandium, the number of electrons in the 3d and 4s orbital is 1 and 2. Removing three electrons from its d and s orbital forms a very stable inert gas configuration. It loses 1 electron from d orbital and 2 electrons from s orbital to form a Sc3+ ion.