In the first transition series, the elements which do not exhibit variable oxidation states is/are

Variable oxidation states are not present in scandium (Z=21). Every element in the d-blocks has a different valency or oxidation number. However, because scandium's ground state d-orbitals are only half filled, scandium does not appear. The 3d and 4s orbitals of scandium have 1 and 2 electrons, respectively. A particularly stable inert gas configuration is created by taking three electrons out of the atom's d and s orbitals. To create a Sc3+ ion, it loses one electron from the d orbital and two from the s orbital.