which element in the first transition series do not exhibit variation of oxidation state and why?

Sc 1s2 2s2 2p6 3s2 3p6 3d1 4s2

Basically the 3d and 4s levels are so close in energy for Sc that energy necessary to remove 4s2 and 3d1 are about the same so you see only +3 oxidation state.