To determine which element among the given options has only one possible oxidation state, we need to consider the electronic configuration and the common oxidation states of the transition metals listed:
Scandium (Sc): The electronic configuration of Scandium is [Ar] 3d1 4s2. Scandium typically exhibits an oxidation state of +3. Once Scandium loses its three valence electrons (one from the 3d orbital and two from the 4s orbital), it achieves a stable noble gas configuration of Argon ([Ar]). Therefore, Scandium most commonly shows only one stable oxidation state of +3.
Cobalt (Co): Cobalt has an electronic configuration of [Ar] 3d7 4s2. It exhibits multiple oxidation states, including +2 and +3, due to the ability to lose electrons from both the 3d and 4s orbitals.
Nickel (Ni): The electronic configuration of Nickel is [Ar] 3d8 4s2. Nickel can exhibit oxidation states of +2 and +3, similar to Cobalt, due to differing electron arrangements that can stabilize these states.
Iron (Fe): Iron, with an electronic configuration of [Ar] 3d6 4s2, also shows multiple oxidation states, primarily +2 and +3, as the loss of electrons from the 4s and 3d orbitals can stabilize these oxidation states.
Based on the above analysis, Scandium (Sc) is the element that primarily exhibits only a +3 oxidation state. This is because Scandium has a strong preference for losing its three valence electrons to achieve the stable electronic configuration of Argon, and it does not commonly exhibit other oxidation states.
Conclusion: Among the options provided, Scandium (Sc) is the element for which only one oxidation state (+3) is readily attainable and stable.
